Dont buy a stick (arc) welder, those things arent worth their weight in dog shit.
Get a "suitcase wire feed" welder with the hook ups to use an inert gas. I would definately NOT get a gas less one. It might cost more and more to operate, but the quality and strength of the welds is absolutely worth it. I believe Lincoln and Miller both make them and depending on which brand you get they are $250-$300. They are portable, easy to use, and make decent welds... my dad had a guy build him a flatbed trailer for his racecar and he did the whole thing with a suitcase welder. That bitch has been hauling all sorts of heavy shit for 6-8 years and there hasnt been a single problem. My dad bought one, but hasnt gotten around to using it yet, here is the one he got and I would recommend you get:
http://www.sears.com/shc/s/p_10153_1...&sName=Welders
Oh and a local welding shop should have it for cheaper, dad got that same kit dealy for $250.