Not that I know of, the best work around is hitting up Google Flights, but even that doesn't make things easy.

Quite possibly my favourite Google product, surprised it has lived this long

It's showing its age unfortunately. For my last set of flights often the price displayed was not available after clicking through on google or on the airline's booking page and flight combos on the airline's sites that I was looking for wouldn't come up in the search :/

Duffel is the best one I know about. Not directly for consumers but good for platform businesses who need an API.

Platform business go through the GDS ( Sabre, Amadeus ) directly just fine. They have the best kind of api

I honestly can't believe there isn't a SF based startup that is already doing it.

The usual issue of flight booking APIs is, that those flights are expensive. It's what travel agencies or travel departments in companies use.

There isn't any money in building api for a platform somebody else owns. At best you do a travel management system for corporate stuff. That kind of a startup definitely exists, funded by YC about ten years ago

You have to get the data from a GDS and it looks like Sabre offers one already [1]. That said I don't know if just anyone can sign up for it.

[1] https://developer.sabre.com/product-collection/mcp-server