Recommendations for open source flight database/API

Question

As a passion project, I would like to experiment with an algorithm I made to find cheap international flights, and make a prototype. As a student, I do not have much money, so I cannot rely on a flight API that is very expensive. Is there an API or database that displays current and future flights that is inexpensive/free? My only requirements are that the database has fields for the flight number, place of origin, destination, time of flight, and airline. Thank you!