I worked at GetThere/Sabre for a few years. There is no public, free API for this information. There is no "all in one" Computer Reservation System out there. You have to go through any number of CRSs depending on which airlines you want to search.
For example, orbitz seems to still use the Galileo CRS. That CRS gets its data from a number of airlines, but not all. I'm also certain that no access to these CRSs would considered "affordable".
https://en.wikipedia.org/wiki/Computer_reservations_system#M...
For example, orbitz seems to still use the Galileo CRS. That CRS gets its data from a number of airlines, but not all. I'm also certain that no access to these CRSs would considered "affordable".