To keep it simple I'll stick with $$$ comparison for now.

Maintenance of a bike, if you have the resources (bike manual, internet, fellow cyclist, etc.) is VERY low cost especially if you don't run to the LBS for every little thing. Learning to be self-sufficient is quite rewarding.

Within the last month I've built up my new primary bike. The cost I pay for gas within 2 months would be the full cost my bike build + some. This includes commuting to the store, around town, and work. I like that trade off.

Monthly maintenance cost is so low it's almost negligible;

$5 bottle of lube that lasts me a couple months for several bikes.
$10 bottle of polish to keep several bikes shiny and clean.

And that's pretty much it. All minor adjustments can be done on your own and larger repairs that you don't feel you can handle can be done at the LBS. Obviously we can't predict the future and there may be unfortunate events that force you to replace components, but hey it's going to be a lot cheaper than replacing stuff on a car.