well the place i work could get it done for $50 if i remember correctly if i did the sandind and burning off of the old paint but for others they usually charge about $150.. it all depends on the work if its aluminum we have to sand blast it to get it clean which cost more...
My neighbor owns a powder coating business and did my old wheels for free becuase the cost of doing it is soo low. But I think he said he would normally charge between 50 and 75 a rim. But you also have to factor in the cost to get your tires taken off and put back on, big-o charged me 100 total to have them taken off and then put back on afterwards.
Same for me hell, galveston is even far for me being that I live 40 miles north of Baytown
EDIT I bet if you checked on www.houston-imports.com that you could find some information on it. They are always getting their wheels powdercoated It's worth a try.