You may be able to find some used works on eBay for that. I got some triple rate works for 200 off eBay. Took me a few months of checking everyday to snag a pair cause they go quick at that price.
Banshee shocks are a minimal upgrade over blaster shocks...so pretty much a waste of money unless you are broke . I picked up some fox sled shocks on ebay and had them re-valved ard charged for my weight and the blaster . Cost me under $200. Rides like a dream
Banshee shocks are a good upgrade especially if you're a larger guy, but if you plan on GNCC racing, stock yamaha shocks won't cut it. They just slow you down and put you in a world of hurt. Grab the 400ex shock and KOR bushing from HPM and look for a good set of Works shocks from a blaster or banshee. Should be able to find something from around $130-$200 but the ones that are cheeper probably need rebuilt. Which might not be to bad because then you could get them adjusted to fit your weight and to handle the gncc.
But whatever you do, DO NOT get any cheap shocks like these!