4 Steps for you to follow.
http://www.smileytools.com/splashPage.hgVisit that site, Pick one, Buy, Weld.For the cheapness, I have heard and seen good things from their units. And being TIG, you can get much better welds at lower amperage. ARC is suicide trying to do bodywork with, trust me. I have seen several turbo manifolds welded up with one of their welders, and if it can hold up to the heat of a turbo, it will work for bodywork. Thing is, TIG is harder than MIG or ARC, so it will take practice to be able to use good.Speaking of being "powerfull enough to weld 240sx sheetmetal" You could just about use a 9V battery. No really, sheetmetal period is easy to burn through if you dont know what your doing. But TIG's are very adjustable, with no wire speed to worry about since you feed the wire by hand.