what is the least expensive welder i can get away with ?

Get a 220v. Although some 110v welder will claim that they can weld up to 1/4" material, I am not convinced. For welding in cages and subframe connectors a 220v welder will insure that you get the penetration necessary for a sound weld.

Lincoln, Hobart, or Miller are all excellent welders and will serve you well for years. I'd get their 180 unit. Hobart calls there 180 unit 187, but they are all basically the same.

As for HF, I own one of their 220 units. It welds nice. I'd buy it again. Is it as nice as a Miller et. al.? No, but it was 1/3 the price. Personally I think the HF is as good as the ones sold by Eastwood and others. HF has just updated their welders. I'd get this one if I were buying again.

http://www.harborfreight.com/180-amp-migflux-wire-feed-welder-68886.html

As others have said, get a bottle of 75% Argon and 25% CO2, the difference in quality is night and day. Though the benefit of Flux core is that you can weld outside, you can't weld outside with inert gas, as the wind blows it away leading to weld porosity.

Final note, the NHRA will not certify a cage welded with flux core. As someone with some understanding of welding processess I KNOW that flux core welding can create sound welds, and is used extensively in structural welding, so their refusal to certify cages flux core welded is dumb.

Regards,

Joe Dokes