Re: Fabrique Nationale Browning 25 cal. Model 1906
Unless the gun has some special markings or is in a presentation case, top value would be around $550 and that is if it is like new. In average used condition (70-80% original finish) but fully functional, they bring around $175-250.
With a minor differences in the safety and takedown system, the gun is identical to the Model 1908 Colt Vest Pocket .25 auto, and most parts will interchange.