Well first off what Model Year X5 do you have?

If it is 2010 or 2011 then you what is known as CIC iDrive. This system uses a HDD based system so you would need the whole BMW software and hardware kit (ISIS, ISTA, ETK etc), which with the Siemens server costs 10k+. On average this costs around $400-$500 for updating and programing.

If you have a 2009 or earlier E70 X5 then you have a CCC iDrive, and this is DVD based. Dealer's and all other official sources charge $200 for updated disc's (maps by TeleAtlas). To update all you need to do is to change disks.

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On Order:
2014 BMW X5 xDrive 35d- Space Gray-Canberra Beige Dakota Leather-Fineline Oak Wood Trim-ZDA/ZCW/417/4FF/4NB/5DL/688

Current:
2013 BMW 535i GT- Neptune Blue-Venetian Beige Nevada Leather-Fineline Matte Wood Trim-ZCW/ZVP/2ST/3AG/416/677
2005 BMW X5 30i- Kalahari Beige-Sand Beige Nevada Leather-Dark Burl Walnut Trim-ZCW/ZPP/ZRC/508/522/609

Former BMW's:
2010 BMW X5 xDrive 48i
2003 BMW 745Li
2001 BMW X5 30i
1995 BMW 525i