The problem with DU guns is that the only distinguishing feature of most of them is minor DU embellishments. There are some very high grade DU guns, but the Winchester 120 isn’t one of them.
Add on top of that the fact that the 120 was never a terribly desireable pump gun in the first place. And it’s a youth model, so the pool of potential buyers is limited even further.
In new, unfired condition, you could probably get $300 out of it if you’re lucky and find the right buyer on a good day. More realistic is the $200-250 range, IMO, and that would be only for a buyer who finds appeal in the DU aspect. Of course, there’s always the chance that somebody out there has one and is looking for another, or had one as a kid and always regretted trading it off and would have no problem shelling out $500 or whatever to ge another one. But I wouldn’t get your hopes up.
Grouse.