well here local the bottom feeder scrap yards are giving $0.01 per LB for steel scrap  i would figure electric motor scrap to be around $0.20 - $0.25 per lb.

That's a pretty wide open question JL.  Especially without even a picture to go by.

Supply and demand, proximity to you (especially if you are in need of one), engine condition, generator condition, overall appearance, actual age (can be determined from serial #), and little things like are there any leads with it, electrodes, is it on a trailer or just the unit, etc.

Sorry, I wouldn't even hazard a guess.  Hopefully some of the guys that are always buying and selling can be of more help.

He Is In Control, Have a Great Day,  Brent

I went and looked at it and its a little rough, no rust, it is a SA 300 and it is a 4 cylinder diesel on a homemade two axle trailer I failed to check make of motor. You have to manual set the high idle before you weld, it has a handle you pull and set in a notch. Makes since they didn't have electric high idle in that day. It welds like a dream, I have never welded with a machine that smooth. The code is 7858
I made him a offer of finishing a gate entrance he started, (he cant weld worth a damn I'll say that) he turned that down so I just told him if he gets ready to sell to give me a call.
The part about machine not welding was operator error, he was trying to use 7018AC and 6011AC rods on magnetic oil field pipe. I sure thought about telling him it was junk and beyond repair but could not do that.
The guy is a foreman at a lignite plant here in Lincoln Tx (Alcoa plant) he bought it and a D8 dozer from a contractor that didn't want to haul it back north, said he bought it for practically nothing so if he finishes that gate job I am going to hit him up again.
And to be that old no oil leaks at all. The valve cover gasket has a small seep and one or two other places but no visible leaks.
Oh, the hour meter 375 hr. if that is correct. I think it is because the machine has been repainted and you can see paint flakes on the meter it's self. It was yellow original, that's the color under the latest yellow paint job. 
Thanks