jlp smacked it square on the noggin...
Start with a B-Square mount (very nice stuff) and a Bushnell scope.
A B-Square mount for the 870/870 Express is priced as follows in Cabela's:
Black -$39.99 Mossy Oak - $49.99
They come complete with 1" rings.
Simmons offers a really cool turkey scope with a "Pro-Diamond" reticle. Cabela's pricing is as follows:
2x32mm Matte Black - $74.99
4x32mm Matte Black - $79.99
1.5-5x32mm Matte Black - $104.99
1.5-5x32mm Realtree Camo - $79.99 (not sure wh this is cheaper)
If Bushnell is the direction you prefer, they offer a "Circle-X" reticle that would work wonderfully for turkeys.
Sportsman 1.5-4.5x32mm Camo - $69.99
Trophy 1.75-4x32mm Matte - $99.99
Trophy 1.75-4x32mm Camo - $119.99
Good luck in your quest, and let us know how it turns out!