Man, there isn't an inverter on this planet you're going to repair for a couple hundred bucks
I've been working on them for ten plus years and have learned the hard way how that story goes. What he isn't telling you is when the main board failed, it took the power modules and input rectifier along with it. Sure, sometimes you get lucky and pick one up that really does have just a simple problem and it was thought to be something much more serious. This usually happens when a machine comes in the tech has no familiarity with and after doing the prescribed checks in the manual, gives up and says it's too expensive to repair.
Generally speaking, control and interconnect board for machine like this are going to start in the upper $600s and just go up from there. A quick check online shows boards for that machine easily costing over a grand a piece.
That's just counting the board. Of course, if any other components are damaged, the price goes up. Plus, some machines will need to have one part replaced to see if another is bad. Put a brand new board in a machine with a hidden problem, guess what? You just blew up a thousand dollar board to find that out. I've had enough board heartbreaks to know that you're seriously rolling the dice on something like this.
There's a reason the guy is ditching them on CL. He likely got them for nothing from an employer or cheap at auction. Sure, if you knew your way around these machines and had some experience it may be worth picking them up in hopes that tou may be able to make a couple good machines out of them all.
Revisions play into things too, and sometimes machines that have been manufactured for a number of years may have extensive revisions made to their internal components, basically rendering used parts interchangeability between certain model years impossible.
Believe me bro, I've cried the blues over stuff like this enough to know its a huge risk at the asking price.
Say $500 for them all? Maybe....
IMHO of course