What is the value of a 1921 silver dollar from the Morgan mint?

To clear things up, "Morgan" refers to the coin's designer George T. Morgan and not to a mint.

Morgan dollars (1878-1904 and 1921) were struck at the then-existing US Mints:

Philadelphia, San Francisco, New Orleans, Carson City, and Denver (1921 only)

Please see the Related Question for more information.