Ryan Cohen is an attorney here in town that does these. You can look up his service at www.ProtestTax.com He seems to charge a reasonable rate for his service.
Engaged Ryan for 2 properties in Atascosa, straight forward, easy and nice, knowledgeable guy as well as gal that answered phone a couple of times. Will check back in after results, but we are already low (vs others) so have tenoeree expectations.