I work at
Mahany Welding Supply. It sounds like you have a bad trigger switch on the gun itself. Like you said, the contacts on the switch are probably bad. Although I can not give you the part numbers and prices for things right now (my work is closed today), I will get back to you by Thursday. My work is able to UPS parts to you if needed. It is ironic that you mention the Hobart Handler 120. I believe we have one on the showroom floor right now that has a clearance tag on it. Ill get back to you on that as well.
I suggest taking the machine to a Welding Supply near you. Many places will look at machines and fix them for a cheap cost to the consumer. I hope this helps.