I see the pipe heading up above the frame of the picture. Does that unit "reside" there and is the exhaust passed outside the building, or is it "portable" (in a sense) and just happens to be sitting in it's present location
What are the voltage outputs? 120? 240? or higher?
Does it have single phase and 3 phase output?
These specifications can help you determine the ballpark value.
The whole unit may actually be in good condition, but just need some TLC.
Take even more pictures and send them to the companies you contact.
Assuming it has been sitting a long time, it will at least need to have the fuel system serviced and need a new battery. An oil change would also be wise. An inspection of the wiring would also be in order.
When new, that was a serious piece of equipment and was not cheap.
I hope you can get it working for a reasonable cost. Let us know how things work out!