Try to find a fish 'warehouse outlet'. I have one I use for fish whenever I can. It's an hour drive away, but worth the wait. They often have a hundred plus male and female Bettas of every color and tail-type available. The one I use keeps them in tall cups (to keep jumping-accidents to a minimum) and the place is so over-heated I have to take off my sweater when I go in. The warehouse-type places are good, because they often breed their own fish or buy from a close breeder, and have a constant supply for low prices.
Examples? Bettas are 1.99, occasionally they mark them out and sell Crowns for 2/9.99 and other types ranging 9-34 dollars. Corydoras of all sorts- Julii, Speckled, Albino, Pygmy, Panda- ranging from .39-3 dollars. Discus for 19.99, pairs of Killies for 11.99, huge Goldfish (I love this, because it keeps people from thinking their half-inch Goldie won't grow. See that huge sucker over there, the one that could EAT YOUR SON? That's Goldie in a few months.) for 7.99. Not itty Goldfish, but big ones. 5-6 inches.
Yep. Warehouse outlets. Go there, now. Find one, and frolic! =D
If you can't... Find a non-chain LPS, and ask if they order Bettas in. My LPS can order in Doubletails, Crowntails, Deltas and better Butterflies for double the price of a normal Betta.