Price is variable, depending on a lot of factors, including...
Finish- Any dings or scratches?
Age- Of little importance with 870s.
Condition- bbl pitting, scoring, any rust, smoothness of the stroke,trigger pull of less than 4 lbs and clean,etc..
Choke- Tubes are best in the long haul, but a fixed Full is what my Trap 870TB has. I'm not busting some targets now because I'm at 16 yards and using a Full choke. Upside is I'm holding closer and when I do go to a more open choke, my scores should improve.BTW, I got a price for converting to tubes and doing the forcing cone today, w/o any tubes it'll run about $110.
Pretty wood counts also.
A Wingmaster with good wood, a pad, and in good shape round here will go for $200-275.Special models like slug guns, Trap guns and fancied up ones run higher, of course.
If that one's in good shape and takes tubes,I'd snap it up for $250, tho I'd probably first offer $225.