How much does a gameboy cost and where can i buy one?

i am not a big gamer but i love the pokemon games so i just want to by a form of the gba so i can play the pokemon games. i am thinking of the gb micro because i just want to play ruby, fire red, and maybe emerald. where can i buy a micro and how much does it cost? also, what are the pros and cons of the gb micro? and no i am not spending 150 bux on a ds.