The Adler family had a dream. And it became reality during a 78-day cross-country trek in a luxury RV—which they completed on only $47 of diesel fuel. The used, 40-foot, 1997 RV, called the "Freedom Machine," was able to accomplish this feat with the help of Frybid parts, which equipped the vehicle to run on waste vegetable oil. The conversion kit the family purchased included new fuel tanks and filtration equipment, so that they could fill the machine at any restaurant and drive away.

The savings aren't quite as substantial, though, when you consider that the Adlers spent over $100,000 on the RV and conversion equipment. The trip was supposed to last three weeks, but ended up lasting 78 days and costing 6-year-old Julia her tooth-fairy money to get the family through the final toll booth. You can read more about their cross-country adventure on their website Liquidsolarpower.com.