For a marketplace knowledge base, the cheapest model for a text summarization API is the one that answers from the right passages on the first attempt. Compare complete workflow cost, not a provider's isolated unit.

The least complex option is a small provider-neutral adapter around one summarization contract. Keep the marketplace data model, prompt policy, token accounting, and retry rules in your application. Keep provider-specific request and response shapes at the edge.

That design answers the cost question more honestly than a static list of model prices.…