I don't know any specifics about the Killeen area. Mostly, prices for wet suits should be retail $150 - $200. If you find anything outside that price range, that's a red flag. Buyer beware.
I will use my 5 mm down into the low 60s temp. You can easily make a 5 mm work into the upper 70s temp. I think I have even used my 5 mm into 82F water. Having said that, this is my usual suit profile:
82F and above: I use a 3 mm even in the caribbean
78 - 82F: Kind of a nebulous region. Maybe a 5 mm. Maybe a 3 mm.
65F - 78F: I use a 5 mm wet suit
60 - 65F: I might use a 5 mm wet suit. Depends upon my mood.
65F and less: I use a dry suit but that's not an option for everyone.
I suspect you could be big boy and use a 5 mm down to about 58F or 60F. Otherwise, I would be a big boy and use a 7 mm down to about 46F. Anything lower than that and you are crazy unless you are diving dry.