Hi Mark,
I would think for the $500-600 budget you could find a wire welder in the 175 amp range. I bought a 135 Hobart for about $399 and it came with regulators and short hoses for gas bottles(no bottles came with it). It will most likely come with self sheilding fluxcore wire already on it, at least mine did.
Give a look at some of these other suggestions that have been mentioned and you might come across a better machine for the same money.
John Wright(I wish mine had more power sometimes)