I'm also a newbie. I started welding to work on car bodies, like you want to do, but in my case, it's to keep my Volvo 240s alive. I started with OA, and taught myself with lots of practice while I was unemployed in 2002. Someday, when I have time, I'll take a course at the local technical high school. They concentrate on stick welding, which I don't really need for my hobbies.
OA works on older cars, but takes a lot of practice to master. I'm still a long way from "master", but I can make OK welds when conditions are right. An OA set can also cut and braze, and is a good source of heat for bending or anything else. The downside is it is slow and it causes a lot of distortion in sheet metal due to the large heat affected zone.
Earlier this year, I bought a MIG, and quickly found out that it is perfect for automotive sheet metal (solid wire with Argon/CO2) and plate up to 1/4" (with flux core). It is fast, distortion is minimal, and it can be used on newer cars with high-strength alloy bodies. But, I can't braze or heat things with it.
For cost, one of the portable OA kits with small bottles can be had for under $300 on web and at the big box stores. The 10CF acetylene bottle doesn't last long, refills are about $20. My MIG (Lincoln ProMIG 135) was purchased at Lowes for $457, and my 60CF bottle of C25 (Argon/CO2 mix) cost $116.
For strictly automotive use, I would go with a MIG. I keep telling myself I should have bought that first. But, the OA torch is a very versatile tool. Using the OA torch, I learned a lot about how a the puddle of molten metal should look and behave, and that helped a lot in learning MIG.
I have a stick welder ($35 yard sale special), but I've never used it.
Hope this helps.