A lot of airlines now let you pay over time for your tickets with sites like Affirm and Klarna. I like that because I can then afford to get a better seat and actually have money for my trip. Sites like Booking.com and Expedia will give you choices from a variety of airlines. If you are flying internationally you will need your passport number to book your ticket. It's always worth it to get some kind of flex ticket so that you can change your dates but even with that type of ticket it may still cost you money. If I'm not planning a last minute adventure I think the planning if 1/2 the fun.