A border stack is usually %50 border, %25 JRT and %25 Staffy. Although where my pup is coming from there is border terrier also. So it would be double border/borderjack/borderstaffy.
I've met a couple dogs from there, and they are amazing. All are CERF and BAER tested, and some are also hip and elbow tested. They are all raised in a very stimulating environment, and all have great tug drive. The breeder requires references, he will not place a dog if he does know someone you know, ect. And there is usually one of their pups on the top flyball teams.
I would pay what I plan on paying because of this. I want to be sure I am getting a healthy dog. And I can't be sure with a shelter dog. Although I do love shelter dogs, I don't want to have to wade through them to find a suitable dog. But in two years, if I did find a shelter dog that would fit, then great! But I would still be getting a puppy from this breeder.