My best advice is, don't go to a SCUBA shop. There aren't any paintball places that can do it near in Austin, so I brought it to a SCUBA place. The blew both burst discs on the reg and all internal o-rings requiring a complete rebuild which they did not pay for. They also complained the whole time about how inconvenient it was to have to test paintball equipment. For any Austin residents wanting to avoid a bad experience getting a tank hydro'ed, this was Dive World on 620.
There are a couple places I found online where you can send it yourself. Most places do this anyway and charge a markup. Here is an example (it's what I will be doing myself next time):
That's about $30 once you add the extras for reg removal/reinstallation and shipping. I'd google around some.