As of May 11, 2012 -- ethanol (adjusted for efficiency) and gasoline are exactly equal ($3.00) on a wholesale price comparison.
Per numerous Sources (DOE, EPA), E-10 (10% ethanol) has ~3% less efficiency than E-0 (zero ethanol). Ethanol on a "net basis" has less BTU content, but higher octane.
-- Wholesale Ethanol prices (pink line) are from the Chicago Board of Exchange.
-- Wholesale Gasoline prices (blue line) are from the Chicgo Board of Exchange.
-- Retail Gasoline prices (red line) are from Bloomberg's survey of national gas prices.
-- Real Time Daily Trading Data on energy products.