The most common pricing question for blockchain API usage: should you pay as you go, or commit to a subscription? The answer depends on your usage pattern more than on price-per-unit.
When you need Bitcoin data in your application, you have two fundamental options: query a node's JSON-RPC API directly, or use an indexed API built on top of the blockchain data.
Bitcoin fee estimation is one of those problems that looks simple until you handle it in production. Simple sat/vB tiers break down quickly when you need to handle stuck transactions, vary by transaction type, or send hundreds of transactions efficiently.