I rally crossed my stock focus an now need to replace my entire suspension set up... Was going to anyways cause it was factory and now I'm gunna upgrade too SVT but is recommend at least a skid plate, and rally ready suspension. Try hot bits. But you'll need to have a custom built skid plate as nobody sells them aftermarket. Also I'd find cheap snow tires rather than rally tires. Won't last as long but are much cheaper. As for skid plate I'd run 1/8th inch and have 3 attachment points on each side with one inch tubing to make it stronger.
Hope this was helpful
Rally Revolution #00 (Leader)
2012 Blue Candy Metallic SE Hatch
2001 ZTS Rally Car