This is exactly the problem L402 protocol solves.

Instead of free tiers that get killed, or subscription tiers that are overkill for small projects, what if you just paid per request via Lightning?

L402 = HTTP 402 (Payment Required) + Lightning invoice. You request data, pay 10-50 sats per call, get the response. No account, no tier, no billing.

For blockchain data specifically, this model makes sense. You only pay for what you use.

We wrote a guide on how to set this up for any API (both as provider and consumer): https://docs.lightningenable.com/premium-guides

For your immediate need, check mempool.space - they have a free API that might work as a Blockstream alternative.