sigh. too many other posters (pedex, skijoring, more?) already beat me to it.
Gas is CHEAP CHEAP CHEAP. My cheapest bicycle cost me over 50 gallons of gas (2004 prices). Our tandem cost us 550 gallons of gas (also 2004 prices).
We're going to look at a little pickup truck tonight that will cost less than 500 gallons of gas, plus burn less than my diesel pickup (which cost me nearly 5000 gallons, though is only worth about 2000 gallons now (current prices)).