Just because the gun is old and mil-surp doesn't automatically make it a "collectible" weapon.
With real estate it's "location, location, location." With many guns, especially collectibles, it's "condition, condition, condition." There are plenty of "shooter" guns out there (such as a mil-surp but not in pristine condition), and many of them perform very well, indeed.
I've had a number of WWII military-surplus weapons over the years and the more common ones -- including a Soviet-captured Luger (with all numbers matching number except a re-numbered side plate) showing some wear.. I didn't hesitate to shoot those guns.
That Luger, despite a badly corroded barrel near the chamber, was a tack-driver. I think I paid about $325 for it, from a local gun shop which had 15 or so for sale in the late 1990's. Parts for many of these guns are more easily found than parts for U.S. guns made in the late 1990's -- probably because there were so many of them made and so many of them still around!
If you have an old Luger like my Soviet-captured Luger, you might win some shooting competitions if you do your part..