Well, the larger cities in Texas will no doubt have a number of small esoteric shops that sell tarot decks. But I don't live in a large city, so all I can tell you is this - seek out the nearest Half-Price Books. They will never have a large selection of decks, but they will always have a selection of decks at really good prices, most often still new and shrinkwrapped (that were warehouse remainders, etc.).
Hastings is a chain with locations all over Texas, and every one of their stores I've been into has a decent selection of decks - usually better than Barnes & Noble and Borders, in fact. If you go into a Hastings store, ALWAYS check the bargain bins and shelves too - I've found many a deck for only $4.95 that way.
You'll find Barnes & Noble locations all over Texas and they are pretty good, although lately they've been going more towards oracle decks and cutting back on their tarot selection. However, if you peruse the bargain shelves near the front of the store, there's usually a pile or two or three of various remainder tarot decks. And as for Borders, I've never found much there, but your mileage may vary. You aren't likely to find a Borders outside of the major cities, though. The Borders nearest to me (about an hour away in the Woodlands, Texas) has fewer decks than my nearby Hastings and Barnes & Noble stores, and they keep them behind glass in locked cases, so browsing is difficult.
Good luck with your tarot shopping!
Edited to add: If you get the chance to go shopping at one of the big outlet malls, such as the one in San Marcos, make sure to stop in every bookstore there. Although you aren't likely to spot more than 2 or 3 different decks in the Waldenbooks and Borders and other book outlets, you can bet they will be available for extremely good prices.
