185k on a set of plugs.I do hope you are kidding.The 100 K is for optimum conditions and is a stretch.At the shop Ive seen cars with 100 on the plugs and they still look decent.Then ive seen them with less and they look bad.No matter what after lots of miles the gap opens and electrode straps start to go away.Ive had cars in that would not run and pulled plugs and there was pretty much nothing left to the end.On the Hemi Ram we changed then at 30K.Used platinums and a dab of antisieze which should be standar on any aluminum head.That and some diaelectric silicone on the boots.coil overs etc.500 depends on what they are doing etc.Seems pricey for plugs but irediums are what like 8 bucks each if it has them.Ive remember sssing lots of threads come out with plugs on aluminum heads because of high miles and no antisieze.On reason they said at first to use it then not to then to use it.Seems guys were loading the threads with antisieze.No need just a bit and it will be happy.Rocky