I took my 2010 Prius for it's first non-Toyota service at 30,000 miles to an independent garage. They changed the oil and filter and told me they used synthetic oil and the car needed a special filter. They charged me a total of $92.95 (including a tire rotation and tax). They said everything else was fine. My gas mileage seems to have gone down from an average of about 50 mpg to 47 mpg. Could this be due to something they did at the garage? I checked the tire pressure and it's fine. Also did I pay too much? Thanks.