Jim McClaren with StrathKirn, Inc. is preparing some excellent corn facts resources.
Here’s a graph from the first one showing “the real cost in chained-2007$ for corn feedstock based on proportional allocation of grain (starch) and conversion rates to ethanol (saccharification and yeast process).” The cost is obviously declining.
In the fact sheet which you can download here (Word doc) he concludes:
Despite recent increases in nominal price for corn, the overall trend remains down and hence corn grain remains a very attractive feedstock for ethanol production. At present, and excepting sorghum grain, there are no other large-scale commercially acceptable feedstocks, and it is doubtful that any economically viable approach can be developed within the fore-seeable future. Thus, it might be advisable to ensure that corn receives the R&D attention required for continued improvement.