I've talked to folks that have done a lot of rally-x and dirt road rallys and they all say that winter tires just dont' cut it like a proper rally tire. They all say, that for the hassle of getting a winter tire, just find a rally racer who is selling his used set of real rally dirt tires. It's said real rally tires performance - especially in regards to lateral grip - is amazing.

That said, there's no cheap 15 allloy wheel for the WRX. If you have a older impreza, there might be more options.