It's difficult to measure the full cost of transportation, as it includes everything from gas/food to time to pollution to accidents and as many other factors as you can quantify. Shoes! Bike chains! New car! Cleaning off that mysterious scunge that collects on the edge of bus seats! The good news is that there are also positive effects, like increased health and the benefits that come with that, like (for many people) increased work productivity.
This chart gives a crude overview, but there's a deeper discussion of the quantification as well as a nifty tool to calculate costs and savings for particular commutes in Vancouver.
Warning: some calculations include use of Canadian health care, so that factor will be bafflingly more difficult to calculate for those of us south of the border by, for example, making cycling somewhat more expensive (because society there will pay for the medical care you need after an accident) and possibly less beneficial (because while much of the medical cost of air pollution is covered by Medicare and Medicaid in the US, some is not). It should be close enough for an interesting comparison.
Hat tip to +Piaw Na