I got mine from Dover Saddlery for just about $100. I don't get to use it nearly enough, as I don't really have a horse to vault with right now. I was using my aunt's appyXbelgium, but with show season underway I don't have time to drive two hours each way very often, and my horse is just a narrow little TB, who I don't think would act very kindly to me standing on her back.
Good luck with vaulting; it is really fun.