The Remington 1100s with fixed choke skeet guns are very well thought of and highly sought after. They have very special chokes, which are very long and produce very nice even and uniform patterns, maybe better than any other gun at any price. If it's a true skeet gun, it will be marked Skeet-A or Skeet-B, on the receiver, the B being only a better grade of wood. The true 20 ga skeet guns are built on the std weight receiver, same as 12 ga guns, , not LT-20.
It depends on condition. "Good shape" means different things to different folks. Some might call a gun with obvious blue and wood wear and multiple nicks and dings "good shape", and another might expect a like new gun.
An obviously worn A, but still in good mechanical condition might go for $350-400, and a minty B in original box might bring $800-900.
If it's an ordinary field gun, $250-400.