My monthly commute is 560 miles.
I average 49 mpg on my F650GS (dunno why so low). That’s 11.42 gallons a month. Assuming $3.99/gallon (regular gas), that’s $45.60/month or $547.20/year.
I no longer own a car, but using the numbers from the Saturn that I donated last August:
I averaged 25 mpg. That’s 22.4 gallons a month. Assuming $3.99/gallon, that’s $89.37/month or $1072.51/year.
So I save about $525 a year ($43/month) by riding.
Now, if I could only ride the XT to work, I’d only spend $31/month ($384/year) on gas for commuting. 😉