This all really depends on what your priorities are, and how comfortable are you financially.
FWIW, when I went from driving to cycling to work, the costs more or less were even. Constant flats, 2 sidewall tears, buying gear (which never seems to end) and the uptick in eating were probably more than the cost of gas. Now that I have things dialed in its probably cheaper, but was much more expensive than I was expecting.