While the price of those small mig/wirefeed welders is enticing, buy the largest (highest amp output) wire feeder your budget will allow. The small machines are fun when you first get them however, when you get into the middle of a large project you will quickly find their limitations and you can forget about doing any quality frame/fabrication work. True mig (using unshielded wire with a shielding gas) will give a higher quality weld, less spatter, better penetration and the ability to weld the thinnest of metals. Also, FYI you can weld cast iron with standard mig wire. I've welded quarter size holes in exhaust manifolds with great success. Just lay wire back and forth over the hole until you are able build up a solid weld then grind down smooth inside and out.
