The Soda Gallery stocks a ton of both common and hard-to-find sodas. Most fall into the $2.50 price range. The store also carries those cardboard six-pack caddies, and the owner will gladly help you curate your six-bottle collection should you be the type who is inept at decision making (i.e. me).
The coolest part of the store, in my opinion, was the myriad of bottle openers for sale. After you buy your soda you have the choice of at least 10 different tools for removing the cap.
(in the Bishop Arts District)
408 N. Bishop Ave. #101
Dallas, TX 75208
214.946.SODA