Has no one mentioned a TIG welder yet??
For a beginner they are much more user friendly and are easier to control the amount of metal deposited.
The weld material is not as hard as mig and can be planished flat more easily before grinding/sanding.
Probably more expensive than a mig but results are better. Try watching you-tube , "SLG Classic cars " and "Khos designs" will show you, with a TIG, just how it can be done.
You only need 35 to 40 amps to weld car body steel.
Argon can be sourced from most of the gas bottle suppliers.
Thanks Steve, assume the 30-40 amps needed applies whether using a MIG or TIG welder? Will watch the video you recommend but am signing up for a city and guilds stage 1 welding course which covers both MIG and TIG methods and can then decide what works best for me.