Vladimir,
The "Bulgarian" that was for sale on Gunbroker is a custom made assembly of parts from different guns. The frame is probably from a German military piece made after late 1913 (can be dated because of the stock lug). The receiver and toggle assembly are from a 1908 (M11) Bulgarian Luger. The barrel is an aftermarket replacement and the entire gun has been refinished with a salt blue and a set of reproduction grips installed. It is a very attractive item but in no way original. What little collector value it has stems from the fairly scarce Bulgarian receiver and toggle assembly. As it is, it is valued only as a "shooter" and top dollar would be around $800 because it is so nicely done and the long barrel is nice for shooting.
I hope this answers your questions
Ron