About $20 at a Fire & Safety Co. in Austin, TX. If you go through a Scuba Diving shop, it's about $65, then they only take it to the Fire & Safety co. anyway.
I just recently had 2 4500psi 88 tanks done and it cost me 35$ for both .the fill was free or included with price soo I guess it was more like 17.50$ air included each. The company I use also does my scuba tanks and he seems to do better on price the more I use him.