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

I bought this one a few months ago.

http://www.northerntool.com/shop/tools/product_200306073_200306073

It welds sheet metal sweet, buy a bigger spool of wire and hook it up to 75/25 gas.
Good enough for home use and should last a long time.
I am a state certified Mig, Tig and Arc welder.