I was going to suggest possibly High School also, that is where me and a few friends learned. There is also a local coop type learning facility here that you could go to half the day in highschool or even take night classes when you are older to learn trades like this. In college we had to weld and use a plasma cutter and were graded on it so this was another learning area and I know some trade school/ smaller colleges will over night classes to learn this stuff but as you have found there is not a lot out there. As mentioned above practice practice practice! Mig is definately the easiest to use, I always liked arc welding but also is more practical for larger pieces of metal and isnt too applicable to the auto world outside of fabrication of frame parts or larger parts. Mig welding pretty much will do anything you need to do. The link above for the Millermatic is a a great one. A good friend of mine has a Millermatic 135 which runs on 110v and is a great little mig welder that lays down a really nice weld, but it is up to you also. Tig welding is my favorite but is pretty hard to learn. It definately allows the most versatile welding spectrum and once you get the hang of it you will love it. It is great because you can pinpoint small things really well without having to overheat all of the material to get the job done and it really looks nice after you get the hang of it. It isnt the best for filling in voids and takes forever to do lots of volume or to weld really thick pieces with but mig or arc cover those areas well. Call around a few highschools and ask if they offer any after-hour classes to learn, the worst they can tell you is no.
