110 mig is, imo, best for sheet under 16 gauge....beyond that the bigger 220 machines can usually be turned down enough for 1/8" plate....up to 1/2" and generally multiple passes when you get that thick. If you have alot of welding of 3/8" or thicker, you wanna step up to 3 phase 575 which of course you wont be able to do at your house. Anything thicker than 1/4"/.250 is pretty rare on cars so youll be fine. Take your time and do lots of practise passes before welding your final product that way you dont cock up when youre welding in/on the car.

Stay away from the Canadian Tire Lincoln mig welders.....pay the extra money and get an american made unit that has a metal wire feed system....ive seen some of the cheap welders with plastic feeds and you WILL regret every minuet of owning it.

If you can spend up to 2k....go to Praxair and get a multi process unit with stick/tig and a plasma cutter....most stuff on cars can be done with stick and then you have the option of tig as well if you want to learn that.