I have a cheap $50 bushnell 4x32 sportsview on my mossy 12 gauge. I had bought that scope for my marlin 22, and I needed a scope to try on the shotgun. I mounted it with $7 Tasco rings, and hit the range.
That scope and rings are still on there 8 years and an untold number of shots later.
There are dedicated shotgun scopes out there, but most cost more than $100. A straight 4x scope will normally hold up better than a variable, and you shouldn't need anymore than that for the ranges a shotgun will shoot.