SCORE just joined BITD in allowing a "door slammer" class for UTVs. You can basically race an almost bone stock car now in these classes. Just need some basic safety stuff like harnesses and nets. No high ticket items like fuel cells, etc.
Hard to answer a question about what to do to a car for racing without a budget in mind. My approach would be totally different if I had 100k to spend than it would be if I had 50k to spend. Just talking about the car, not support.