How much money do you get from selling a used Game Boy

first of all your question is vague there are lots of gameboys GB,GB play it loud!GBP,GBL (japan only),GBC,GBA,GBASP,GBM

I'm assuming you're talking about a gameboy, gameboy pocket or gameboy color

Gamestop:Wont accept it its too old
Pawn Shop:1-3$
Person/Ebay: You will get more money if you sell this in person but facts are facts not many people are still interested in gameboys and if they are they will want it in good condition it will be a lot harder to sell in person 5-20$
5$ anyone will pay five bucks for it
10$ probably
20$ overpriced