I was going to guess about $150 myself… As far as plug replacement, I have not noticed an issue on the Optis, but if it is caused by the crap running all over the motor (fuel lines, etc) I would likely remove the bottom “bucket” part of the cowl. For a while I ran 12 plug heads (land and sea) on my XR6, and getting to the lower plugs was tight. I just spent about 15 minutes to take the bottom cowl off (two clamshell pieces) rather than fighting (and occasionally breaking the insulator) on the bottom plugs. Ive changed them with little cursing needed on an Opti, but the right set of sockets and extensions and u-joints makes it a little easier. Work on enough Japanese (and American) cars under 10 years old and the Opti plugs seem easy. Try the back plugs on a Ford Excursion2008 Pantera Classic2014 Mercury Pro XS 200