I checked for NAV in my 5-series and was quoted $5K as well - way too much, and BMW NAV isn't necessarily the best or easy to use.

I just picked up one of these NAV systems from one of my resellers, they're on eBay as well.

http://cgi.ebay.com/NEW-NAVMATE-HORI...QQcmdZViewItem


I have no relation with this particular seller, but $200 is a killer price for NAV. I have it here and it looks like a really decent unit.