Silver dollar's minted in 1921, commonly referred to as the Morgan Dollar, are valued at approximately $20 in circulated condition. In uncirculated condition their value can more than double.
As with any coin, the overall condition will determine its final value. Most pawn shops and other non-collectors will commonly offer the lowest possible value in exchange for a coin. For a specific pricing based on actual wear, it's a good idea for a coin collector to take any coin to a professional coin dealer. However, in order to command the highest possible price for a particular coin, having it graded by an accredited and reputable grading company is best.