I have had a go at repairing a couple of the clark type migs and boy are they crap. Personally I have a Sterling mig which has hardly been used and a Pico 140 inverter which is a great little machine. I think some of the newer inverters will go to 160 amp will running off a 13 amp plug but you wont get much more than that but I wouldnt fancy trying to run it at a high duty cycle or it will probably cook the plug never mind blowing the fuse. I think that is the main reason why people go for the small cheap kits is that they can run them from a 13 amp plug for a while.
We have a load of old Murex 500s at work that will be at least 20 years old and still give a great weld. They dont look very good but do the job.