You can get a decent road bike for about $1,000 – mine was $800 new. I ride almost 10,000 miles per year. 80% of that is shopping, commuting, going to visit friends, etc. – i.e. things I would otherwise have to use a car for.
My van gets 20 MPG, so I save about 500 gallons – or $2,000. I figure I save another $2,000 in automobile depreciation/maintenance costs. So the bike pays for itself in three months. Plus I don’t suffer road rage, don’t pollute, and don’t give money to scummy middle eastern and South American dictators.
Someday I will move to Holland and give up the cars completely. I can’t wait for that.