How do I find out how much baseball cards are?

I have all kind of baseball cards from 1988 - 1994. Cal Ripken, Ken Griffey Jr, Nolan Ryan, Mark McGwire, Ken Griffey Sr., Craig Biggio and many many more. They range from Fleer, Donruss, Upper Deck, Topps, Score and so on. Could someone tell me where I can get the price of them. Thinking about getting rid of them and do not want to sell them too cheap.