Underground Comix are known for using different prices, covers (art or color variations) and/or interior content to distinguish between printings.
1st print 1970 had 1.50 USD cover price and was a magazine sized fanzine self-published by Richard Corben.
2nd print 1970 (actually December 1971) has 0.50 USD cover price. This version is indexed here.
3rd-4th print have 0.50 USD cover price and are believed to be indistinguishable from 2nd print.