I just bought one of those ridiculously expensive rear mount bike racks that mount to the rear bumper tow hooks. If anyone is looking for one at a fairly decent price, you can find a new one on ebay being sold for $541, shipping included, by Passport BMW (my local service shop).
I've spent days looking for a better price online and can't find one. Here's the link to the last one:
http://cgi.ebay.com/ws/eBayISAPI.dll...m=200912232676
If its sold and you're still interested in getting one then check back in about a week. I noticed they re-posted after selling the last two. You may find a slightly better deal if your parts place is running a 25% or 30% sale on accessories.
Also, there is someone in Kansas City, Kansas selling a new one on craigslist for $500. It's probably negotiable. Here's the link to that:
http://kansascity.craigslist.org/bik/3651341298.html
It's an expensive rack, but I figured that I could sell it for $350 or $400 once I sell the X6, so my cost of using the rack eventually would be a lot lower.