It's been the dirty little secret of Prius owners for years. While their cars are extremely reliable, they end up paying more for repairs when they do have to be made. Now, a study confirms what had been rumored for some time: Repairs on the Prius cost more than for cars of a similar size. To be precise, 8.4% more.

There's good news, though, if you're considering buying a Prius. The difference was most pronounced for earlier cars (2001-2006) and seems to have vanished almost completely for the two most recent model years (2007 and 2008).

The study attributes the difference to the small number of Priuses sold in early years, compared to the hundreds of thousands of, say, Civics and Accords sold each year. Fewer Priuses on the road reduced the supply of repair parts available from "recyclers"--what we used to call junkyards--requiring more of them to be bought directly from Toyota. Manufacturer parts are almost always pricier than used parts, so the average repair cost crept up.

The study compared repair costs from the Prius with those of gasoline-powered economy cars as a whole. Five cars--the Honda Accord, Honda Civic, Toyota Corolla, Nissan Sentra, and Hyundai Elantra--make up 68 percent of that group, collectively selling many hundreds of thousands each year.

A second piece of the study compared costs for cars that came in both regular and hybrid versions, including the Honda Civic and Toyota Camry. Again, the hybrids cost more, but the difference was much lower--just 3.8%--because most parts were shared across both versions, with only a few unique to the hybrid model.

The study is from Audatex, a company that automates processing for insurance claims. You can read the report for yourself, here.

[Photo from Flickr user Mike Hussein Cohen.]