having welded with all sorts of machines, here is my take
stay away from the flux cored units, yes they cheaper and don't require gas
but they are basically stick welders that use tiny rods
for doing the body panels you want a gas mig,
recently i picked up a hobart handler 130 with blown rectifiers for 70 bucks
32 dollars for a pair of easily replacable silicon rectifiers and it is up and running
using mixed gas it is probably the nicest light guage gas mig i have ever used. it is a 120volt machine
the flux cored machines will do the job, but the needed chipping and cleanup is a pain in the rear on sheet metal
the gas shielded migs are a dream in comparison.
if you look around you can find nice used millermatics that run off of 220 for under a grand, i have seen them for far less
today on craiglist there is a 220 volt machine for 450bucks,,, you just can't go wrong with one of those.
i have no idea what your budget is, but you would be far better served to spend a bit more on a good miller, linde/ltech/esab, hobart
or lincoln machine,, although the lincolns usually bring more money an in my opinion aren't worth the premium.
a good gas mig will be the last welder you will ever buy, and likely will be the machine you use the most.
tig has its place and for some things it is the best way to go,, but for a first machine that is very versatile go with the mig.
next
use a good mixed gas when welding steel, linde/praxair used to sell a product called stargon which was a proprietary mix
and made for beautiful welds
don't skimp on cheap wire either, new machines come with an e2 wire, which is adequate for very clean well prepared steel
a step up to an e6 rated wire which is allowed makes for great welds on less than nice steel, rusty, scaley stuff
the price differential is about 15% more,, so in the scheme of things it isn't much more to pay for what you get.
i bought a linde 225 mig back in 1983, it cost me around 1700 bucks back then and i have used up several 44 lb spools of wire in it
and it still works as well as it did the day i bought it, it will weld sheet metal all the way to 3/4" plate in a single pass (properly prepared of course
in spray arc mode) and it was the best investment i ever made in a tool bar none.
a few years ago a friend of mine picked up a miller onan powered ac/dc 250amp welder, complete with a spool gun (mig aluminum or steel)
complete with 100 ft of leads, torch, bottles and hose real on a trailer for 750 bucks! i used it with the spool gun and found it to be a fantastic
machine.
and yes i did everything i could to try and talk him out of the setup
if you look around you will find some really nice deals on used machines,, don't shy away from a larger unit 220volt
you will end up with a machine that will do so much more than the economy 120 volt units that you buy at the box stores
and last you the rest of your life,,, and probably never lose a dime on it either when you are old and want to sell it.
bob g