Must you use stock / un modified frame attach points? A cheaper version is to use an R6 shock or even better....an aftermarket R6 shock. But you may need to modify some attach points or the shock, depending on the shock. Check out the internet or rzrd500 for more info.
I have a few R6 shocks with the bushings for an RZ in them. Let me know if you are interested. Its a good shock. I just replaced it with a Penske.