whatever you are willing to pay... That sounds flippent, and is not meant that way too much. But go to the gun auction sites, visit Simpson's LTD and other sites, (See
http://www.lugerforum.com/lugerlink.html )
Otherwise, it could be $700 or it could be $1100, or more, if a matching mag. You don't find a matching mag, so that can drive the price up another $100-$300...
Pictures would help a lot and if hypothetical, then my answer above fits.
Ed