You are mistaken. 

It is price per BTU, combustion, and  thermal efficiency that must be factored.  Diesels have inherent enrichment  issues that cannot be overcome without additional combustion enhancers or alternative fueling such as HCCI/RCCI (even ultra high pressure common rails have limits).   Ethanol is at or below BTU parity in most of central US. 

Don't trust me; ask the MIT professors or ask the UW Engine Research collaborators for theoretical combustion efficiency of each fueling regime. .