Video Game Systems

I want to know how much is a fare price for a used gameboy advanced game and say you buy 3 or 4 games should you get a deal? Which is better a gameboy color or game boy advanced and how much would you pay for each used? Also what about used kids books how much is fare for those?

I heard that it can play CastleVania 3, a game that most Famiclones cannot play, so does that mean that the entire NES library will work with no problems, or are there some games that won't work, making the actual NES a better investment? The SNES and Genesis aren't important, but I'd like to know as well.