I just did plugs on a 2015 Hemi truck.

The plugs alone were $200 for a good brand.

The passenger side isn't too bad but the PCM had to be removed from the bracket to get to the rear plug and the heater hoses kept being in the way.

The drivers side was more of an issue. The brake booster and firewall were in the way of the back 3 plugs. You simply couldn't get the required length extension in the space you had. I had to position a socket in the plug hole, add a 3" extension and lower the socket down then add another 1.5" extension. Reverse the process to remove the socket and use a flexible claw magnet to remove the plugs that didn't stay in the socket.

Took less than 2 hours and that included cleaning the throttle body & Air filter housing along with the air filter replacement. Around here a $400 to $500 job since labor is $100 an hour.

The dealer wanted to to tuneup my wife's gran prix for an unreal price once. I said I can put plugs in for $40 what else do you do. He said we also hook it to a scan tool and check the idle settings. I said "they aren't adjustable what do you do if it isn't right?" He just smiled and "said nothing because we can't change them." At least he was honest about that.