Eh, I don't see how it could more expensive really. At least in my case.
14.5 miles one way. 29 miles round trip. Car gets around 26-27 mpg. So I save a gallon a day. Which as of today in my area is $3.49. So I don't have to pay for parking or anything but $3.49 * 5 days = $17.45
Lets say I just do it twice a week still = $6.98 which is about the cost of one inner tube. $6.98 * 4 weeks = $27.92 not including oil changes, anti-freeze, and other fluid replacements.

So in summary. I bust a tube once every couple of months and it's about $6.50 on Amazon. But just by travelling by bike twice a week throughout the years I've saved 27.92 * 12 months in gas = $335.0 + an oil change