I have a car and a 125cc bike which costs peanuts to run. It cost me £700 inc the bike, CBT, gear and insurance and I made that back in 5 months in fuel savings. Now it costs me £12 every 2 weeks to do 250 miles
I used to get 95-100mpg from my YBR 125, it was great money wise, but not a lot of fun. I now get 58ish mpg from my SV650. I save £15-£17 per week by taking the bike instead of the car, so that covers running the bike (Tax £70, insurance £90, M.O.T. £25) plus helps towards the money I spent on passing my test, new riding gear and anything the bike needs.
It's not a short term gain, but that was never the point, I can leave work when I want now, I don't have to plan my time around traffic.
I only have a car for ferrying the kids around when my wife is at work and for when it snows and taking the bike isn't the best idea. My wife is looking to get a job close to home where she doesn't need to use her car, if she does, one of our cars will be gone.