High gas prices are one of the driving factors behind the increase in used car prices this year. An Edmunds.com's analysis reveals that the average price paid for a three-year-old used compact car was 10 percent higher in July than it was in January. The overall change in price for all vehicle classes was found to be 4.3 percent higher.

"In 2008, consumers reacted to rising gas prices by running away from SUVs; in 2011, they reacted by running toward small cars," said Richard Arca, a used car analyst at Edmunds.com "This year's pricing trends are also affected by the March earthquake in Japan, which for some time made it very difficult to find, for example, a new Toyota Prius or Honda Civic. That created a very aggressive market for similar used models."

Not surprisingly, the analysis also found that the average cost of used SUVs dropped 3.2 percent in the same period, which shows that consumers are shopping more economically, but are not as troubled by gas prices as they were in 2008. That year, between January and July, the average price plummeted 23 percent for large, traditional SUVs.

Drivers who are concerned about gas prices can use car warranties to help pay for maintenance that could improve fuel efficiency. Getting regular fluid changes, tune-ups and tire rotations can help improve the fuel economy of a vehicle.