Trap grades go for a premium compared to stock Wingmasters and a good bit more than Expresses IF, and only if, they're in good shape.
Deer guns, like waterfowlers, get dinged up.
Like Kudu, I recommend just getting another 870 and making it a dedicated rough duty shotgun.
Also, trap wood and long barrel put the trap 870s close to 9 lbs empty. You may find that rather heavy 3 ridges away from the truck.
And, a complete used 870 with deer barrel may be found for around the same price as a new barrel.
HTH....