show jumping, stadium jumping and jumpers are all the same thing.
As far as jumpers breaking down it manly has to do with the huge amount of stress put on their legs, that's why wearing jumping boots with a lot of support are so vital.
I don't do jumpers so I don't know much about how long they last, sorry.
As far as pricing goes a lot factors into. Show experience and level, training, conformation and of course naturally ability. A horse with good bascule and nice tidy style over the jumps is desired. A horse with a more hallow back over jumps won't be able to lift their legs as high. http://freelanceinstructorsdiary.blo...-dressage.html
^^Go down and look at the ideal conformation of a show jumper.
"For jumpers, the emphasis should be on hindquarters with a good length from the hip bone to the point of the buttock for power off the ground. I look for correct angles from hip to buttocks to stifle to hip. This triangle should have sides of similar lengths. A long, more level quarter equals more rrear-wheel drive. The length from stifle to hock should be similar to the length from the point of the hock to the ground. Longer-backed horses often have more scope."
The A circuit just refers to a pretty high level show. Basically there are local shows, C shows, B shows, and A shows in the hunter/jumper world. The competition is usually better, they are usually more crowded, and of course, a lot more expensive.