Jeff, 

My first thought was to ask $200 for the bare center tub and axles castings. I'm guessing it weighs around 500 - 600 lbs. I haven't found an accurate price online for clean cast, but at $200 that puts the price at .33 per pound (approx).

My intention isn't to take advantage, just get a fair dollar amount that makes everyone happy. Without a doubt I do want to move it out of the shop. I intend to call tomorrow and get the currrent price per pound (or ton) for clean cast. That would give me a better idea if I'm asking a fair price from a buyer perspective. Even if I find that the price per pound is more, I'll stay at the $200. At that I admit, I will have broke even. I wouldn't think cast price would be under my estimate (I really think its at least twice, but its been a couple years since I last scrapped anything) and if it is, well I guess I'll adjust accordingly. 
If I'm only going to get scrap price, I might as well sell it to where it can be put to use. 
He can always scrap his rear when done and recoup some cost as well.

I'll get in touch by phone soon. 

Jeff