If you are looking to save money, don't buy a vehicle off-lease unless you want to pay interest for 7-8 years on a single vehicle.
If you can't afford to purchase a brand-new X3, do this: turn the lease back in, and purchase a similar X3 off the used car lot. Lease turn-ins are not the dealer's property to resell, they get sent to auction, where dealers purchase them. When you purchase your vehicle at the end of the lease, you don't have much negotiation room; however, if you purchase someone else's lease turn-in, there is often substantial negotiation space. Moreover, (and I'm not sure why this isn't offered with yours, but presumably because the vehicle doesn't change hands to BMW and to a dealer when you buy out the lease), many BMWs are CPO and have a warranty/maintenance thru 100k miles.
I bought my 2008 CPO back in 2012 with 58k miles, warranty and maintenance covered through 100k or 6 years (Feb 2014). After negotiations and trading in my E46, I paid $12k for the car.