It depends on where you go and if you have the reg already removed as some facilities charge a small fee for removing and reattaching the reg. Generally anywhere from $25-$40 as that can include shipping of your tank to and from the facility.
You can use a dive shop locally however be warned that many dive shops do not have the proper tools or knowledge on how to remove a paintball reg. So you run a much higher risk of them damaging your regulator then a paintball specific hydro test facility.
Hydrotests aren't based on the make of the tank, rather, the place that is doing the testing will price it.
Over here, they charge us $25/tank.
My 68/45 cost me the same as my 48/3000 (why I hydroed the latter is beyond me)