The XC3S50 is the only Spartan 3 so far available, so you won't find any other board available yet. I did see one 50 board that was available for $99 though...
Those development kits comes available sometimes next february. And XC3S50 might not be for sale very long time. I got this information form sales representavite last october.
I think you should think XC3S400 kit, because you can program it with free xilinx webpack ise (unless you have alot of money).