Is cycling cheaper than driving?

If I asked you if driving a car more or less expensive than riding a bicycle? What would be your answer? A car is more expensive you would say, way more..and you would be wrong. To finish the job of bruising your ego I will present mathematical proof...or perhaps I am providing proof of how big a geek I am. Ether way here goes.

First the easy part.
My car gets 30 mpg, gasoline costs $4 a gallon.
My car costs 7.5 miles per dollar. 

Now the deceiving part
Gasoline contains 31,000 kCal of energy.
I can ride my bike 20 miles and burn about 800 calories
That's the gasoline equivalent of about 775 miles per gallon. Cheap right!

Wrong!
Food costs $0.75 per 200 kCal. Gas is a whopping $0.025 per 200kCal.
So (20 miles/800 kCal) * (200kCal/$0.75) = 6.6 miles per dollar. Less mileage than a car per dollar. See I really am a geek. If you check my math your a bigger geek than me.