I bought mine from kellycodetectors.com and they've been pretty good so far. I would recommend them.
You just need to research and ask questions on TN. A lot of helpful folks on here.
Go to the websites of each detector manufacturer and check their list of dealers. As large as Houston is, there MUST be a dealer in the area. If there actually isn't one, then PM JOE(USA) on this site, he's a dealer and post a lot, especially on the Tesoro thread.
I am in Houston as well and got my ACE 250 from KellyCo. I have been pleased so far. I didn't have to drive all over town looking for a dealer as they ship directly to you.