I bought mine at Advance Auto parts as well just make sure they are double platinums. The total price was I think about $70 plus tax but believe me it's worth it. My engine light was on for a whole year and my car would always shut down randomly. I decided to change my plugs when it finally shut down in the middle of a 4 way stop. Ever since then, the car is a million times faster, shifting gears seems preety different I had no idea spark plugs would even make a difference when it came to shifting gears but it did. My engine light is finally off. I took it to Advance to hook up the machine to check for more codes and there are none. The spark plugs are well worth it. I changed out the plugs by myself with no one's help. Yes I'm a female 22 I'm used to working on hondas but I'm not going to lie, this German car was a beeeeeeeeetch until I figured out how to change them. My hands are cut up so if you have a child with little hands that would help you soooo much more! Make sure you get 12 plugs...yes 12 plugs. I almost died when I found out it needed 12 plugs but The Xfires are the Mercedes SLKS just with a Chrysler body and those also require 12 plugs as well as some of the Jags. Other than that you will be happy once the new plugs are in you'll notice a HUGEEEE difference. As soon as my camera comes in I'm going to make a vid