Id would opt for buying a lot of games off of ebay, if the price doesnt get too bad, you can find some hidden gems within these
I ordered a set of 10 NES games off of Yahoo auctions once, it included Mega Man 1, I paid 19 shipped for the package, I turned around after the MMAnniversary Collection was released and sold my cart for 16 on ebay
You just have to be resourceful, I find others at flea markets, and rarely from pawn shops and goodwill