Moody, he started off working on VWs (that's how I got to know him; I'm kinda a VW nut), he had his own shop, did any sort of VW/Audi repairs. He now owns a strictly Audi shop, and does a LOT of welding work for the autocross and rally racers across Colorado.
My good friend Bryan
Big Red Racing took his old Civic, and had Moody weld in a roll cage for him, and they have worked together to make the little Civic rally ready.
From everyone I have seen that's installed a roll cage into their cars they all wish they had simply bought a car with an SCCA qualified rollcage already welded in, and then just taken it to Moody to have him weld in extra supports for that extra safety bonus. I would suggest checking out
Rally Classifieds for such things, used to be Ben's Rally Page.
I would suggest to start off going to RallyCross events, you don't need a rollcage, and you get to really know the people (Rally community is a real tighknit community). You'll get to know who has what tools, who can weld, whose welding jobs you can trust, and so on.
I don't even have a car to race (silly 4x4's), but I still try and get out to any event I can. Sometimes, someone may need a navigator, or a service tech, or even someone to go out to a press spectator spot and shoot video/take pictures. It's always fun, and there's been plenty of times where if I just had $5K laying around I could have bought someone's old rally vehicle and started racing right then.
Definitely call up the SCCA in your state, and see when/where they are having rally crosses and races, and what the regulations are. Keep asking questions, I love talking about Rally!