In my opinion, $2.57 per cart is not too shabby at all. Perhaps it's based on my location, but I rarely find NES games for less than $5, despite the title. There just must be something about living in Canada that makes gaming more expensive (*sigh* Darksiders II Wii U deal at American Best Buys).
Why is it that so many people seem to own Castlevania II: Simon's Quest, yet not the first or third game? That always makes me wonder. Anywho, there are plenty of titles in there that I think would make a solid base for an NES collection. Black Box games like Baseball, Ice Climber, Pinball, Soccer, Super Mario Bros. and Gyromite, Nes Play Action Football and NES Open Tournament Golf, Castlevania II, Double Dragon 2, Blades of Steel, Solar Jetman, The Tecmo Bowl games, The Ninja Turtles games, Tiny Toon Adventures, The Track and Field games, Commando, Strider, Spy Hunter, Super Spike V'Ball -- all titles I would be happy to have in my collection.
And of course, you can always use the shells of the games you don't want for something else.