This is a "good" choice for "weekend welding use"...it is one of the models I poured over before buing a miller online... IT IS MADE BY MILLER...some of the inner, moving, parts are plastic and therefore subject to wear/slippage, etc....before those made of metal... Look at the duty cycle factors...look at the amp rating vs what you are going to be doing with it AND notice that it ONLY runs on 220v AC 1-PH power... You can get that power from "most" industrial gensets of 5.5kw or higher output...making your welding "mobil" to some degree, eh?... Parts are available all over the place...since they come from Miller...one of the 2 BIG names in this Mfg area.. I opt'ed for the "duel voltage" capability, in the same amp rated unit, with a slightly lower duty cycle...The Ironman 210's were orginally selling for $1,200 to $1,550 according to where...they may have been discontinued to be replaced by a newer model/higher base price/unit, etc... marketing dept jazz and all that... IT SHOULD DO 3/8" all day, with say 30% cycle for cooling...you could do 1/2" in some direction/polarity with some deep beveling, again watching your cycle factor.. That switch is most likely about $20 or so...
IF you need such a HD machine for that thickness of material...I'd try $800 just to see if he'll bite and give you a great deal...open it up and see just what is actully broke...you may be able to use some super glue and some plastic, eh?...IF just the "knob" is busted off, and it's not "driven back into the switch body due to impact"...But, do remember, this is a 220v AC machine..and switch...it will have a loaded "spring" feel to it..
Good luck and enjoy,
God Bless,
Mel