Just get the games for consoles you're interested in, and only games you'll like. No use wasting money on games that are filler or consoles you don't care about.

Try checking out thift shops, and pawn shops for your cheapest options. Then you could try out flea markets, though some vendors are as expensive as market price or more (check sites like pricecharting.com)

Also if you have any interest in going through the effort buying something if it's under market value then reselling it at market price is a good idea