I run HyperPros on my GSA and really like them. Check out the Vendor's forum for special pricing. If I'm not mistaken, most suspension companies have 2-3 sales a year.
After researching the price differences between buying used (then rebuilding) and buying new, it was a wash. So, I bought my HPs for just under a thousand bucks. Still a lot of money, though, but they were customized to my inseam, weight, etc.