Ron Guth: The era of the "modern" commemoratives began in 1982 with the issuance of the George Washington Half Dollar (issued to celebrate the 250th anniversary of his birth). Prior to 1982, Mint officials were reluctant to issue commemorative coins because of the hit-or-miss success of some prior commemortaives and because of problems caused when speculators and manipulators attempted to control the market and prices. Fortunately, the 1982 Washington Half Dollar went off without a hitch, and the modern commemorative program was born. Some of the more popular themes in this series include the Olympic issues (offered on several occasions), the Eisenhower Centennial (1990), and the American Buffalo (2001). In recent years, there seems to be a downward trend in mintages of the Unciruclated versions, reflective of either commemorative "fatigue" or a poor economy. Proof mintages are usually higher (often considerably).
The success (or failure) of any particular issue depends on the theme and how broad an appeal it may have. For instance, there is a lot of interest in Olympic issues whereas the 2000-P Leif Ericson commemorative saw limited interest (which translated into a low mintage). Low mintages can translate into higher prices later, once collectors become aware of their scarcity.
Prices for coins in this series are completely dependent on supply and demand, but all are readily available for a price.