It's an ex-German police surplus gun, refinished with a replacement slide and an incorrect left grip. I would not regard that as a "collectible", but these days people will collect anything, including old beer cans and cat whiskers.
An objective appraiser would view it as a mongrel of unknown mechanical condition. If functional, its value is as a shooter only, worth just its intrinsic value-- not some higher figure inflated for "collectibility". In other words, about half the asking price.
Just a personal preference on terminology: I called it a "mongrel" since all of its parts are at least proper for that model. A "frankengun" in my parlance would be a gun made up of parts from different models of guns, like a P.38 with a P4 upper.
M