What is the value of an 1897 US 20 dollar gold piece?

Look on the back of the coin to see if there's a small mint mark letter below the eagle. It may be blank or there may be an S.

Numismedia lists the following approximate retail values as of 01/2011:

No mint mark (Philadelphia):

Very worn condition - $1,580

Moderately worn - $1,620

Slightly worn - $1,640

Almost no wear - $1,686

Uncirculated - $1,760 to $18,230 depending on quality

"S" mint mark (San Francisco):

Very worn - $1,580

Moderately worn - $1,620

Slightly worn - $1,640

Almost no wear - $1,686

Uncirculated - $1,760 to $19,910

DISCLAIMER: The retail values quoted are the best available as of the date shown, but may vary significantly due to changes in the precious metals market. Also the wholesale (buying) price of a coin will be less than the selling (retail) price. A reputable coin dealer will be able to give a more accurate valuation based on inspection of the coin.