I hate to say it, but I think your numbers are a bit off.
One barrel of crude
oil = 42 gallons of
oil which yields 19.5 gallons of gasoline.
http://wiki.answers.com/Q/How_much_g...l_of_crude_oil
Therefore, saving 320 gallons of gas per vehicle per year, times 700K vehicles, would save 224 million gallons of gas per year, as you state. However, this equates to 11.49 million barrels of crude
oil per year (not 5 million barrels).
At $75/BBL this represents an annual savings of $861.5 million.
At this rate the government's $3 billion C4C outlay would be recouped in 3.5 years.
Now what's the average useful life of these new, more fuel-efficient vehicles in the national fleet? 10 years? 15 years? 20 years?