I thought the cheaper MIGs had a manual press type solenoid/valve inside the torch assembly. Changing the polarity wouldn't be that difficult. I'm quite sure there would be enough room in the hose for a gas tube.
A conversion would be possible probably for less than buying a new, but I wouldn't bother unless you can find a cheap second hand or something that has been scrapped with the parts you need still working.
A conversion would be possible probably for less than buying a new, but I wouldn't bother unless you can find a cheap second hand or something that has been scrapped with the parts you need still working.