In my experience stores that sell retro games sell them for waaaay more than they're worth, or they'll sell them for "ebay price" which 9 times out of 10 is also overpriced. That's not counting the 50 copies of Madden, of course.
Anything from the N64/PS1-era and earlier is hugely inflated in price. Sometimes you have games that are actually rare and should be valuable, but then most of the time people assign arbitrary prices and try to sell them and then idiots with disposable income and who have reached the age where they are nostalgic for these games buy them, and then it slowly becomes the standard price. Like dang, Super Mario Bros. for the NES is not worth $20+. And then there's the stupid sellers that think "oh it's an SNES game so it must be valuable", sometimes with the variation of "oh it's an SNES game and it's a good game so it must be valuable", not realizing that Super Mario World, while a good game, is incredibly common so really shouldn't sell for more than like $8,
but no, it should sell for half the value of a brand new game in 2015. And yeah, then there's scalpers that just keep the prices inflated because, as stated earlier, nostalgic shitheads that don't know anything about this stuff will just buy it because they can. And then worst of all you get random price hikes on games because someone popular like James Rolfe or the Game Grumps plays/talks about them and then suddenly they're "worth" like $200 (literally) and the price takes forever to go back down, or never does. (See:
Space Megaforce and
Wild Guns)
There are still quite a few PS1 games that can be gotten for pretty cheap, some of them are really good and a bit unknown. That won't last for long though. And PS2/Gamecube games are starting to rise in price. Wii games are generally still pretty cheap and PS3 and 360 games will be for even longer, since those systems are still kind of going sorta kinda. Right now it's just kind of a waiting game for the bubble to pop and the older games to start going back down in price, but that probably won't happen for quite a while, if it even does.
I still remember the day I got Final Fantasy III on SNES for $2 and
Little Samson for $0.50. Unfortunately, my mom sold that one in a garage sale without telling me
It's unlikely we'll see a time again that we can get these games for ultra cheap.