not sure how the US market is set up, but in europe you can easily get small, affordable diesel cars. We even have little (if not tiny) VW Lupo's and Polo's with diesel engines at work.

Only problem is that diesel engines produce more fine soot particicals (more air polution), so the goverment has put higher road taxes on diesel cars.

the most enviormently friendly solution is obviously leg power and more healthier too. That and public transport is how i get around. If i do need a car, generally for work, i get one from mine boss.