The modifications done to that model 645 scream IPSC/USPSA competition pistol. Maybe someone just wanted a custom 645, but as a former competitor I recognize those as the popular modifications performed on competition pistols. It may have also been modified to be single action only. These modifications raise the question of just how much use has this one seen? I'd want to at least field strip it and inspect it for wear before considering a purchase. If it isn't worn out, and it has already been established that it has zero collector's value, it is only a shooter grade pistol, I'd say it might be worth $400, $500 would be pushing the limits.