Is it cheaper to bike?

Recently I stated that it was cheaper to bike to work (or anywhere) than drive. I based my statement on a GAO estimate that the operating cost of a bicycle was $0.05 a mile and the AAA estimate that the operating cost of a car was $0.26 a mile.  Some people disagreed with the GAO estimate (and I can no longer find where I got it from) so I wanted to figure out, is it cheaper to bike than drive?

First some ground rules. I am making all of the following assumptions:

1. I'm not considering the cost of ownership for either the car or the bike. No insurance. No car payments. No registration. No taxes. I think it's pretty clear that if riding a bike allows you to get rid of a car, it is financially advantageous.
2. I'm assuming you can park for free and you pay no tolls. If you have to pay for parking, I think biking again easily wins.
3. The mileage is the same whether you bike or drive. (Though for me biking is about a mile shorter because I go farther out of my way to catch highways).
4. I'm not counting health benefits for biking, nor am I counting social cost (environmental damage for example) or differences in safety. I'm also not considering time.
5. I'm not counting extra food you might eat when biking. Americans have weight to spare.
6. I'm assuming you don't use your bike for recreation of exercise.

Cost of operating a car.
This is pretty simple to find. I used AAA's 2005 numbers since they're automobile advocates and are unlikely to overstate the costs. They claim that a car depreciates at $0.2586 per mile. The cost of maintenance, tires, gas and oil ranges from $0.121/per mile to $0.152/per mile. I'll use the lower number. Add the two together and the cost is $0.3796/per mile.

Now let's assume you bike 14 miles each way like this guy. That's 28 miles a day for 240 working days. A total mileage of 6720 miles. That will cost you $2550.91.

Cost of operating a bike
This was a little more difficult to find. Some tried to say that biking was free. Or gave a number without an explanation. Just to play devil's advocate I'm going to pretend you need to throw out everything and buy it all new the next year. What will that cost?

Commuter Bike - $550 to $599 lets call it $600
Rack - $30
Light - $94
Tail light - $12
Trunk - $34
Bell - $9
Extra set of tires - $70
12 tubes (one a month) - $60
Multi-tool, pump etc.. - $24
A mid year tune up - $45
An extra set of brake pads - $8
1 bottle of chain grease - $14
Socks - $8
Helmet - $95
Shorts -$65
Pants - $100
Jersey - $40
Winter Jersey - $109
Gloves - $36
Winter Gloves - $28
Shoes - $95
Booties - $50

Now with anything else, you could spend more for these items. But you could also spend less and certainly this is all you need. Add it all up plus taxes and you get $1711.50 leaving you just under $840 to buy extras of anything, pay for extra maintenance and or even splurge somewhere in there. And, I know most of these things will be able to go 7000 miles without wearing out.  So I feel confident that biking is at least 1/3 cheaper than driving.