I love when people get rid of their old games and don't have any idea the value of some of it. I purchased a box from a Co worker, the box had about 40 games in it. It was mainly first party NES, SNES, & N64, it also had a couple PSX games. Really was just the best games(Zelda, Star Fox, Mario, Contract, Castlevania, Mega Man). He only wanted $40 for the whole box, but I have him $75. He threw in 2 NES, 2 SNES, & 2 N64 controllers, all Nintendo Brand, since I paid him extra
One of the PSX games was a black label Castlevania: SOTN, I sold it on eBay during the Double coupon promo for $55. I received $55 PayPal and a $55 eBay coupon for one game from that box. So afterwards I got a ton of retro games for free and I made $35. Can't really ask for a better deal then that.
If I were you, I'd check eBay. Just search NES or SNES and look at the sold auctions and sort by highest price. That could give you a idea.