This issue is a variant of Dr. Atomic (Last Gasp, 1972 series) #2 [1st print 0.50 USD]. There exist further variants.
Underground Comix are known for using different prices, covers (art or color variations) and/or interior content to distinguish between printings.
1st print (April) 1973 has 0.50 USD cover price.
2nd print (1975) has 0.75 USD cover price.
3rd print (1977) and 4th print (1978) have 1.00 USD cover price.
Inside front cover with indicia information at bottom of page.
Sequence ends on inside back cover.