What is the value of a 1919 US half dollar?

Look on the back of the coin to see if there's a small mint mark letter at roughly the 8:00 position. It may be blank or there may be a D or S. (The W on the front of the coin is the designer's monogram and not a mint mark.)

Numismedia lists the following approximate retail values as of 04/2010:

No mint mark (Philadelphia):

Very worn condition - $23

Moderately worn - $97

Slightly worn - $300

Almost no wear - $954

Uncirculated - $1,410 to $16,450 depending on quality

"D" mint mark (Denver):

Very worn - $25

Moderately worn - $127

Slightly worn - $438

Almost no wear - $2,484

Uncirculated - $6,000 to $289,250

"S" mint mark (San Francisco):

Very worn - $21

Moderately worn - $87

Slightly worn - $305

Almost no wear - $1,908

Uncirculated - $3,450 to $48,750