I heard 335 gets plugs at 45k or 50k. I have heard of some owners getting them done under maintenance coverage and some after that has expired, so it's out of pocket. I agree with the above posts, if you can DIY, do it. If not, go to an indy. I got a quote for new plugs from an indy for $350 VS dealer $400, $65 for filter. Some prices may be similar but depends on where you are.
2007 BMW 328I Monaco Blue /// 1999 BMW M3 Titanium Silver /// 2007 BMW 328I Sparkling Graphite (sold)