Wondering about Artillery Luger's Value

[JSLTIGER]

I know this isn't exactly submarine related, but I figured that with everybody's interest in military equipment, somebody on here might know enough about guns (specifically Lugers) to help me out.

My great-uncle fought in WWII with the 100th division, and came home with several souvenirs, including a War Merit Cross, a WWI Mauser rifle, a sword, and a long-barrelled Artillery Luger pistol. Unfortunately, he was killed in 1947 when a drunk driver clipped him on his motorcycle. Today, my grandfather is in possession of these items, and we're attempting to find out the value of the Luger.

As I mentioned, it is a 9mm Artillery Luger, made by DWM. I can't remember if the year was 1916 or 1917, but I do know that it is a low serial number, #503. All but a single part has the same number stamped in it (03), but one has 45 (so we know that that has been replaced and will lower the value). It is in excellent working condition, looking as clean as the day it was made, and it still fires (my grandfather fires a few rounds every now and then). I also know that we have a n original leather holster with a Nazi insignia pin attached to it (although it is in poor condition), but that we are not in possession of the snail 32-round clip or shoulder stock. Anyway, like I said, if anyone has a clue to its value, I'd appreciate it! Thanks!