I'll trade you a gen 2 Glock 17 straight up, even throw in a few extra magazines AND the tupperware box it came in. Probably worth $450 or so...
(me own opinion following... sell off grandfathers bring back Luger?
You're a better man than I sir. Plus, I guess you'll have to change your screen name then too eh?)
Take some good photos. Go over to lugerforums. Post a WTS or WTT (you could do it here as well mind you). A local gun shop will offer you about half of it's actual worth, but that is one method of deciding on a value you can live with.
Good luck. Hope you get something of equal value. (but I has me doubts, some things are worth more than money. IMO again)