some people will give tem away because of thier digging/tunneling habbits. neat fish as i had 1/2 dozen of them in my tank, very hardy fish. i would say about 5 - 20 bucks each depending on if they are trade ins or common stock ect.. i got mine for free with the stipulation that i had to take all 6 to get them at that price
ive got one. id have more, but dont have the room. its busy tunneling away as we speak. the adults look totaly different compared with the juveniles.
just make sure that your rock is hard on the base of the tank though... if the rockwork is on top of the sand, the gobies tunneling habits could cause a rockslide that could collapse on the fish, or fall and crack your tank.