Here is a quick DIY guide i wrote up after having to replace one of my leaky pumps on a 2006 X3 and one of my aunt's on her 2008. Hopefully the photos and explanation will help make it easier for anyone thinking about replacing them on their own:
BMW X3 Washer Pump Replacement DIY Guide
The part linked to there is an original OEM Siemens pump that you can order from Amazon.
Hope that helps the community save some bucks...