Hybrids and clean diesels offer impressive fuel savings over their gas counterparts. But these are sophisticated technologies and often add thousands of dollars to a car's sticker price. In the past, the federal government offered tax credits that helped soften the financial impact of buying hybrid and diesel cars. This spurred sales and encouraged consumers to adopt the then-new technology. But those tax credits ran dry years ago as the federal government shifted its efforts to electric vehicles and plug-in hybrids.

Where does this leave hybrids and diesels now? Are they a good value? And if you buy one, how long will it take before you start realizing the savings based solely on buying less fuel?