is it CDMA? you can always wait for iOS 6, that will have unlock. The developers decided not to bother with baseband 04.12.01, it was originally unlocked but patched later in May by Apple, iOS6 was already announced and they said it is useless to work for a new unlock when iOS 6 will be out so soon and everyone would want an unlock on it.
I got a new iPhone 4, 32 GB, black, iOS 5.1.1 and baseband 04.12.01, I got it for 140$ because the unlock is around 170$, but I'm not unlocking it, I'm waiting a few more weeks until iOS 6 rolls out.
You could try doing the same, ultrasn0w is free. I also wasted 30$ on a crappy unlock on some website that didn't even work, I called their support, mailed them, tried to get a refund with paypal and they refused me, they didn't even comment on that, they offered zero support and my money were basically given to them for... nothing. Quite sad actually.
Don't buy unlocks unless it's factory unlock, which is pretty damn expensive.