Here's where I bought mine from. I bought the SP-100T model and have welded up to 3/16" steel with no problem. Works great for all the bodywork I've been doing.
SP-135T
http://cgi.ebay.com/LINCOLN-SP135T-M...3A3%7C294%3A50
SP-100T
http://cgi.ebay.com/LINCOLN-SP100T-M...3A6%7C294%3A50