there is a local wingmaster with 18" barrel and 70% bluing for $300. i think that's too much, but i don't really know about the 870. i want one because i need a good cqb shotgun that one day, i'll be using for 3 gun matches and also for homje defense. also, just since a member here is making an adapter for it to accept the ar15 telescoping stock, i am even more interested (i was going to get a benelli m4, but that can wait... if they haven't all been sold out yet).
so, which 870 should i get?

I've just started doing EXACTLY what you are doing. If you look in the shotgun section you will find my thread. I bought a 870 wingmaster from a member for $200 yesterday. I'm working on getting it refinished now. Sounds like $300 is too much. I'd keep looking but I'd either stick with a 870 Police or a Wingmaster with their forged receivers then go to a 870 express. If you keep lookin you'll find one. Or try and talk them down.

I even have the same uses for it. Defense first with a secondary role as a 3-gun gun. For near or under $500.