diff --git a/base_client.go b/base_client.go
index bbc5f15..c81052c 100644
--- a/base_client.go
+++ b/base_client.go
@@ -342,10 +342,35 @@ func (bc *baseClient) doGet(ctx context.Context, endpoint string) ([]byte, error
 	return data, nil
 }
 
+// cacheQueryBody reshapes a GET's query map into the map[string]any the cache
+// keys on. Without it every query on one endpoint would share a cache entry and
+// serve another query's response.
+func cacheQueryBody(query map[string]string) map[string]any {
+	if len(query) == 0 {
+		return nil
+	}
+	body := make(map[string]any, len(query))
+	for k, v := range query {
+		body[k] = v
+	}
+	return body
+}
+
 // doGetWithPayment issues a GET, and if it comes back 402, signs the payment
 // and retries. This is used for Pyth-backed market-data endpoints where the
 // same path may be free (crypto/fx/commodity) or paid (stocks/usstock).
+//
+// The cache is consulted on the way in and populated on the way out, on both
+// the free and the paid branch. It matters more here than on doGet: a miss on
+// this path costs real USDC, not just latency.
 func (bc *baseClient) doGetWithPayment(ctx context.Context, endpoint string, query map[string]string) ([]byte, error) {
+	cacheBody := cacheQueryBody(query)
+	if bc.cache != nil {
+		if cached, ok := bc.cache.Get(endpoint, cacheBody); ok {
+			return cached, nil
+		}
+	}
+
 	url := bc.apiURL + endpoint
 	if len(query) > 0 {
 		sep := "?"
@@ -374,7 +399,14 @@ func (bc *baseClient) doGetWithPayment(ctx context.Context, endpoint string, que
 		if !bc.hasWallet() {
 			return nil, &PaymentError{Message: "endpoint returned 402 but no wallet is configured"}
 		}
-		return bc.handleGetPaymentAndRetry(ctx, url, resp)
+		data, err := bc.handleGetPaymentAndRetry(ctx, url, resp)
+		if err != nil {
+			return nil, err
+		}
+		if bc.cache != nil {
+			bc.cache.Set(endpoint, cacheBody, data)
+		}
+		return data, nil
 	}
 
 	if resp.StatusCode != http.StatusOK {
@@ -385,7 +417,14 @@ func (bc *baseClient) doGetWithPayment(ctx context.Context, endpoint string, que
 		}
 	}
 
-	return io.ReadAll(resp.Body)
+	data, err := io.ReadAll(resp.Body)
+	if err != nil {
+		return nil, err
+	}
+	if bc.cache != nil {
+		bc.cache.Set(endpoint, cacheBody, data)
+	}
+	return data, nil
 }
 
 // handleGetPaymentAndRetry mirrors handlePaymentAndRetry for GET requests
diff --git a/paid_get_cache_test.go b/paid_get_cache_test.go
new file mode 100644
index 0000000..f7e69ba
--- /dev/null
+++ b/paid_get_cache_test.go
@@ -0,0 +1,164 @@
+package blockrun
+
+import (
+	"context"
+	"encoding/base64"
+	"encoding/json"
+	"fmt"
+	"net/http"
+	"net/http/httptest"
+	"sync/atomic"
+	"testing"
+)
+
+// countingPaidGetServer serves a 402 on an unpaid GET and 200 once a
+// PAYMENT-SIGNATURE is presented, echoing the query back so a caller can tell
+// two different queries apart. It counts every request it receives.
+type countingPaidGetServer struct {
+	requests atomic.Int64
+	payments atomic.Int64
+}
+
+func newCountingPaidGetServer(t *testing.T, opt PaymentOption) (*countingPaidGetServer, *httptest.Server) {
+	t.Helper()
+	c := &countingPaidGetServer{}
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		c.requests.Add(1)
+		if r.Header.Get("PAYMENT-SIGNATURE") != "" {
+			c.payments.Add(1)
+			w.WriteHeader(http.StatusOK)
+			fmt.Fprintf(w, `{"q":%q}`, r.URL.Query().Get("q"))
+			return
+		}
+		req := PaymentRequirement{
+			X402Version: 2,
+			Accepts:     []PaymentOption{opt},
+			Resource:    ResourceInfo{URL: "https://example.test/resource"},
+		}
+		body, err := json.Marshal(req)
+		if err != nil {
+			t.Errorf("marshal payment requirement: %v", err)
+		}
+		w.Header().Set("payment-required", base64.StdEncoding.EncodeToString(body))
+		w.WriteHeader(http.StatusPaymentRequired)
+	}))
+	t.Cleanup(srv.Close)
+	return c, srv
+}
+
+// solanaPaidGetClient is a Solana client wired to local fakes: no network
+// leaves the machine, and the cache lives in a temp dir.
+func solanaPaidGetClient(t *testing.T, apiURL string, cache *Cache) *baseClient {
+	t.Helper()
+	resetSolanaBlockhashCacheForTest(t)
+	_, rpcSrv := newRPCCounterServer(t, usdcSolanaDecimals)
+	return &baseClient{
+		chain:        chainSolana,
+		solanaKey:    testSolanaKey(t),
+		solanaRPCURL: rpcSrv.URL,
+		apiURL:       apiURL,
+		httpClient:   &http.Client{},
+		cache:        cache,
+	}
+}
+
+// TestPaidGetServesRepeatFromCache pins that a repeated paid GET is served from
+// the cache instead of re-paying.
+//
+// doGetWithPayment used to ignore bc.cache entirely, unlike doGet, so
+// WithCache(true) was a silent no-op on exactly the endpoints that cost money:
+// /v1/pm/ carries a 30-minute TTL, yet every repeat call re-signed and re-paid.
+func TestPaidGetServesRepeatFromCache(t *testing.T) {
+	counter, srv := newCountingPaidGetServer(t, *testPaymentOption(USDCSolanaMainnet))
+	bc := solanaPaidGetClient(t, srv.URL, newCacheWithDir(t.TempDir()))
+	query := map[string]string{"q": "bitcoin"}
+
+	first, err := bc.doGetWithPayment(context.Background(), "/v1/pm/markets", query)
+	if err != nil {
+		t.Fatalf("first paid GET: %v", err)
+	}
+	// One 402 + one paid retry.
+	if got := counter.requests.Load(); got != 2 {
+		t.Fatalf("requests after first call = %d, want 2 (402 + paid retry)", got)
+	}
+
+	second, err := bc.doGetWithPayment(context.Background(), "/v1/pm/markets", query)
+	if err != nil {
+		t.Fatalf("second paid GET: %v", err)
+	}
+	if string(second) != string(first) {
+		t.Errorf("cached body = %s, want %s", second, first)
+	}
+	if got := counter.requests.Load(); got != 2 {
+		t.Errorf("requests after second call = %d, want 2 (cache hit, no network)", got)
+	}
+	if got := counter.payments.Load(); got != 1 {
+		t.Errorf("payments = %d, want 1 — the repeat call re-paid", got)
+	}
+	if got := bc.GetSpending(); got.Calls != 1 || got.TotalUSD != 0.001 {
+		t.Errorf("spending = %+v, want 1 call totalling $0.001", got)
+	}
+}
+
+// TestPaidGetCacheKeyIncludesQuery pins that two different queries on one
+// endpoint do not share a cache entry. Keying on the endpoint alone would make
+// the cache serve bitcoin's response for an ethereum query — worse than not
+// caching at all.
+func TestPaidGetCacheKeyIncludesQuery(t *testing.T) {
+	counter, srv := newCountingPaidGetServer(t, *testPaymentOption(USDCSolanaMainnet))
+	bc := solanaPaidGetClient(t, srv.URL, newCacheWithDir(t.TempDir()))
+
+	btc, err := bc.doGetWithPayment(context.Background(), "/v1/pm/markets", map[string]string{"q": "bitcoin"})
+	if err != nil {
+		t.Fatalf("bitcoin query: %v", err)
+	}
+	eth, err := bc.doGetWithPayment(context.Background(), "/v1/pm/markets", map[string]string{"q": "ethereum"})
+	if err != nil {
+		t.Fatalf("ethereum query: %v", err)
+	}
+
+	if string(btc) != `{"q":"bitcoin"}` {
+		t.Errorf("bitcoin body = %s", btc)
+	}
+	if string(eth) != `{"q":"ethereum"}` {
+		t.Errorf("ethereum body = %s — a stale cache entry was served for a different query", eth)
+	}
+	if got := counter.payments.Load(); got != 2 {
+		t.Errorf("payments = %d, want 2 (distinct queries must not share a cache entry)", got)
+	}
+}
+
+// TestPaidGetWithoutCacheStillWorks pins that a client with no cache configured
+// is unaffected — every call goes to the network, as before.
+func TestPaidGetWithoutCacheStillWorks(t *testing.T) {
+	counter, srv := newCountingPaidGetServer(t, *testPaymentOption(USDCSolanaMainnet))
+	bc := solanaPaidGetClient(t, srv.URL, nil)
+	query := map[string]string{"q": "bitcoin"}
+
+	for i := 0; i < 2; i++ {
+		if _, err := bc.doGetWithPayment(context.Background(), "/v1/pm/markets", query); err != nil {
+			t.Fatalf("paid GET %d: %v", i+1, err)
+		}
+	}
+	if got := counter.payments.Load(); got != 2 {
+		t.Errorf("payments = %d, want 2 with no cache configured", got)
+	}
+}
+
+// TestPaidGetNoTTLEndpointNotCached pins that only endpoints with a configured
+// TTL are cached. /v1/zerox/ has none, so it must still hit the network every
+// time rather than silently serving stale swap quotes.
+func TestPaidGetNoTTLEndpointNotCached(t *testing.T) {
+	counter, srv := newCountingPaidGetServer(t, *testPaymentOption(USDCSolanaMainnet))
+	bc := solanaPaidGetClient(t, srv.URL, newCacheWithDir(t.TempDir()))
+	query := map[string]string{"q": "bitcoin"}
+
+	for i := 0; i < 2; i++ {
+		if _, err := bc.doGetWithPayment(context.Background(), "/v1/zerox/quote", query); err != nil {
+			t.Fatalf("paid GET %d: %v", i+1, err)
+		}
+	}
+	if got := counter.payments.Load(); got != 2 {
+		t.Errorf("payments = %d, want 2 — /v1/zerox/ has no TTL and must not be cached", got)
+	}
+}