Comment by Xcelerate

For flights, SerpApi (to get Google Flights data) in combination with seats.aero pro. I use data from those services with a MILP library where I provide various travel and cost constraints. Runs periodically and notifies me of any good deals. I don't know if my setup actually does much more than the more expensive paid services already out there, but I can at least customize it a lot more to my liking to avoid a lot of manual search effort.