I know there's quite a few 870's out there. I could probably go buy a new one for about $300. I'm looking to sell mine with a 26" bird barrel and a rifled cantilever mount barrel (minus the scope). The gun is a few years old, has a wood stock and no scratches or marks in it. What should I expect to get for it? Thanks for your help in advance.

I just bought a synthetic-stocked one last summer, used with a 28" barrel, for $230. Got a cantilever slug barrel for $180 too a year before that (at the time I was borrowing my friend's 870 until I could buy my own). I guess you could sell it all together for $400 or so unless I paid too much for mine.

Is it an Express or a Wingmaster. 2 3/4" only? 3"? 3.5"?

A lot depends. Could be as high as $650-700 or as low as $250-300.