Cabin,
It's going to be tough to find a good scope for under $125. The thing is that shotguns actually kick more than most rifles. Specifically, a test was done where a 12 gauge Mossberg pump with 3 1/2" turkey loads actually had the same kick as a .458 Winchester! :eek: You would never put a less expensive scope on a .458, so you shouldn't put one on such a shotgun. Now, I don't know what kind of a shotgun you have, but still realize that shotguns GENERALLY need better than average scopes.
In your case, I too would try and look for a used Leupold Vari-X, but a III rather than a II. Leupold's have great tracking and hold their zero. I'm not sure about the parallax issue because I don't know what your average shots are. Then again, most of my scopes that are parallaxed at 100 yards do just fine at 50, so I'm not quite sure what the effect of the whole parallax issue is really all about.
In my experience, I just can't recommend a new scope for under $125. I totally understand your money limit, though, that's why I think that you'll be better off with a good used leupold. Check out ebay - they have great deals there.
Zachary