There are several places in San Antonio that do powder coating. I got a quote from Alamo Crosslink but ended up using Redline Exhaust in Kerrville when I had my sliders done because they were competitive in price and closer to me
They did a great job and I was in and out in < 3 days. All that said, there is probably someone closer to you in Austin, I just don't know who they would be
Make sure you figure sand blasting in the cost of the powder coating. Most places will give you a quote on just the powder coating and will usually want to sand blast as well which can run up another ~$100 pretty quick. Be sure you get a quote for an out the door price.