Yep no saving money with a bike..
a good rear tire: ~27 miles per $1. ~1.85/gallon @50mpg
Front tire: ~42 miles per $1. ~1.19/gallon @50mpg
~$3.04 per 50 miles in tires alone @50mpg.
It does help negate some of the costs that we get good gas mileage...but doesn't exactly put you in the black.
But hey all the fun you get riding it + road rash = priceless