Q u o t e: Liar.
Nobodys talking about any of that, and no you can not get duck hunt or any of those major games you just named for anything less than a few hundred dollars.
I actually busted up at this one. There's this mom and pops store I go to where I can still get the SMB/duck hunt 2 in 1 cart for $2. Dragon Warrior 1 is $5 I think and there's a crapload of SNES, NES, and Genesis titels for under $10, with a few of the more sought after titles for around $40. It's not impossible. (though, I never did see a SNES FF3 there, I did see an SNES FF2 for about $40 to $50 IIRC).
As for DI, I haven't seen it in a game store in a while, but I've never seen it for over $20.