College/HS/ International scouting budgets:
20 million - you'll see the maximum amount of players available to you, and the most accurate projections you can get. BUT you will still miss out on a handful of them, and the projections will never be perfect.
18 million - almost the same quality of projections but less number of prospects.
16 million - about as low as I'd go to put any real confidence in the projections.
14 and below - diminishing returns from here on down. You can still get lucky picking up a player at 14 million, but they won't be what the projections show you. For the most part, when you get bad projections they're mostly overestimates.
For Advanced Scouting, I think you get what you pay for. I say I think because many/most experienced owners Zero it out. Advanced shows you projections for players on teams other than your own, so if you're not actively and regularly trading for other teams' prospects it's a large expense for minimal return. Owners like me trust our own best guesses when looking at those types of players. Or we just never trade for them.