It is conceivable that your car will benefit from a fuel system cleanup. Direct injection engines are known to be more susceptible to carbon deposits than the previous generation of engines because of the way they operate. But $400? No way!
Handle this yourself by adding a bottle of Techron to the gas tank. Do this every six months or so.
Note: Your owner’s manual may recommend you use only Top Tier fuel in your car. Top Tier gasoline is rated to have enhanced detergent properties to reduce or eliminate carbon buildup. If you use only Top Tier gas you can even eliminate the routine Techron treatment. See: http://www.toptiergas.com/