Microfilm and electronic versions will be available for sale ALONG with the free online version (18+ terabytes of data) on April 2, 2012 at 9am.
From a NARA Announcement:
For customers with large data requirements, the National Archives Trust Fund is selling the 1940 Census data on hard-drives and hard-drive arrays. Microfilm copies of the 1940 Census data will be available for purchase from the Trust Fund, as well.
The National Archives Trust Fund will accept pre-orders for the 1940 Census data on hard-drives and hard-drive arrays. Digital copies will be available for purchase as a whole or by individual state.
Pre-orders for the entire 1940 Census and/or for individual states will be sent via overnight mail on April 2, 2012.
If you would prefer the data on microfilm, orders for 1940 Census microfilm can be placed on April 2, 2012.
The complete 1940 census will cost $200,000 in digitized form and $580,750 for the microfilm (approx. 4646 rolls). Census data for individual states costs between $3000-$9000 for the digital version. Microfilm prices from $51,500 for New York (412 rolls of microfilm) to $125 for the Virgin Islands (1 roll of microfilm).
See Also: Learn More About the Trust Fund