Before reading this thread I would have said its worth $1000-1200. That would be based on the cost of buying a new 870P for around $700, second hand Remington 14" barrel for $400. Combine that with how hard the 14" are to come by and perhaps you could get even closer to the $1500 mark. Scattergun Tech shotguns are nothing more than gussied up Express shotguns with a couple of accessories and a nice paint job, yet they cost over $1500, all without the desirable Police Magnum stamped on the side.
If Tacord has a steady supply of new factory 14" Remingtons for $900, well that would affect the market a fair bit and make yours worth less than that unfortunately. Barrels with rifle sights may still command a premium to collectors because they no longer make them that way.
Norincos don't affect the price of the Remington in any way. I can get a 14.5" Norc AR for $700. does that make the 14.5" Colt cheaper? Hell no. People buy the Colt for the name and the quality associated with it.
Mossbergs are a different beast and have their own collector market, they may be harder to come by but does that make them worth more? I'm not sure, I don't think the demand is anywhere near what it is for Remingtons, which would affect the value obviously. They still make these BTW, won't find it on their webpage but then again, either is the 870P. The 870P is on their LEO/MIl page, not their normal retail page.
Wish I could find a 14" 870P for $760, you definitely did well on that deal. Rifle sights too, nice. I have a 14" Rem Cyl barrel, wish it had rifle sights instead of the Trak Lok. One day I'll have Casey install the factory rifle sights, probably give it the Vang Comp treatment too since it's Cyl bore.
Aren't all 870P marked Police Magnum? I thought that any of the older 2 3/4" guns were simply marked Wingmaster?