Ive got two in a tank your size, and I agree with Stir that one is probibly better. Mine dont really get along. The dominant one is out and about all the time but the smaller one tends to hide.
My smaller one has swimbladder issues.. either that or air in its stomach. Reading up on this I see its fairly common in these fish.
I too paid somewhere over $100.. I try to forget how much.
They are a really nice little fish.. kind of punky looking but they dont seem to bother the other fish. I have mine with seahorse and pipefish and a mandarin.
I got mine from Oceanic Corals.