1st print (September) 1972 has 0.50 USD cover price.
2nd print (January) 1975 has 0.50 USD cover price and believed to be indistinguishable from 1st print.
3rd print 1977 has 0.75 USD cover price.
4th print 1978 has 1.00 USD cover price.
5th print has 1.25 USD cover price.