1st-11th printings have 0.50 USD cover price. All printings should say which printing and date.
3rd print says "Third printing, September 1971" in the indicia on page 2.
12th print has 0.75 USD cover price. 13th print has 1.00 USD cover price. 14th print has 2.00 USD cover price.
15th print has 2.50 USD cover price. 16th print has 3.50 USD cover price.