It seems that savings would be increasingly realized the greater one distances themselves from their car, provided both are being used. If someone commutes to work by bike but keeps a car for the other stuff (and fully insures the car), they're not going to save much beside gas. If they ride a lot more and drop the automotive insurance coverage to liability only, they save that plus more gas, repairs, and depreciation, etc. If they sell the car and commute for everything, they save even more.

There's other benefits besides the financial-personal health, the environment, etc. It's worth the cost of building up a good commuter bike as far as I'm concerned.