Eric
Take a look at this web site, Simpson LTD, they have several 1918's for sale, look under DWM guns.
http://www.simpsonltd.com/
Prices you see will be high retail and toward the max a retail shop would charge you if you bought the gun from them. A basic rule of thumb is to take 60% to 70% of that value as what you could expect to get for your gun. This is just basic business 101. Everyone wants to make at least 30% profit, anything less than that and they soon go out of business.
For example they currently have a 1918 much like yours listed for $2250, using my formula that places your expected value between $1359 and $1575.
Pretty much what Ed just told you just arrived at using math and a reference.
If you think this still sounds low, monitor some of the auction sites such as Gunbroker.com, you will see about the same thing going on.
They made a lot of 1918 Lugers, so even though your gun is collectible it isn't rare.
Vern
By the way, welcome to the forumâ??why not just keep the gun, itâ??s a pretty nice one to start a collection with