CAR annual costs:
Ad Valorem: $65
Gas @ $20/wk: $1,100
Insurance: $600/year
Oil/filter changes: $150
Various maintenance: $250
This total: $2,165

Bike annual cost:
Tires: $25-30
Tune-up: $60
Tubes (5/yr): $20
Maint. supplies (grease, cleaner, oil): $15
This total: $125

According to this calculation, I save $2,040. Actually, I still pay for and use the car but a week of bike commuting will save me $20-30 in gas or more.