OK4450's right about the BS 'transverse engine' charge. I have a 99 Hyundai Sonata with a transverse V6, and it costs around $300 or so to get the spark plugs changed by the dealer, largely due to the fact that the intake manifold has to be removed, along with all the parts attached to it, in order to get at the rear three plugs (which is a PITA.) But the dealer doesn't charge a separate fee for the manifold removal, they just include it in the price to change the plugs. To do otherwise, well, it's kind of silly.
Also, many FWD 4-cylinder cars have transverse engines, and the plugs are a freakin' breeze to get at. Any shop that charges a 'transverse engine' fee for cars with easily accessible plugs are crooks.
At any rate, you can probably get the job done cheaper elsewhere. However, before you do, consider if it's really necessary to get this 'tune-up.' Is the car running fine? No driveability problems? If so, then I highly doubt you NEED new spark plugs. Remember, Firestone is after your money, and I highly doubt they check your spark plugs for wear every time you get an oil change.