Keep in mind, too, that bettas can have hundreds of offspring in one spawn. It's a million times better to invest in quality stock and have quality offspring to show for your efforts, rather than lower quality pet store bettas. No breeder in their right mind would purchase a pet store bred betta.
I know what you are saying, but keep in mind the thousands of pet store bettas already sitting on shelves everywhere. If you breed, you should try and contribute to the Betta splenden species instead of breeding stock with scrambled genetics and issues.
There are several breeders, even on this website, that can offer you high quality fish for relatively cheap.