go to any of the several gun forums that he is a member of and post for sale with details of the "extra's" and fair estimate of condition.

I haven't checked recently but reloading stuff used to be available on ebay. Also it might be sold on auction sites like gunbroker.com. To determine real value you have to look at the completed auctions and see what people are actually paying for the stuff, not what sellers are asking for the stuff.

If you can't determine anything from that research, I would suggest that pricing for the presses in good shape should start at about 70% of their new price. The extras might not bring that much unless you sell them individually which is a lot of trouble. If you lump in all of the extras you might get 50% of new value for them. And this is mostly because someone that buys a big package might not need every one of the extras. Plus someone like me would normally be inclined to buy just the press and the bare essentials first, and buy the extras one at a time over a period of time.

dos he have that 650 and of so what dos he need out of it?
looking for used dillon press 650 or 550b