If you're looking for an economical X3, consider either the 2.0d or 3.0d. The 2.5l is a bit of a heavy drinker. Forget what the brochure says, under normal driving conditions, even the 3.0l would use less fuel than the 2.5i.
I had the 3.0l and it was damn heavy on juice in mixed driving. I struggled to get it below 14l/100km.....on the open road it was much better though. Did a trip to Namibia which averaged at about 10l/100km iirc at 140km/h mostly. From whatever I read everyone always agreed that the 2.5l models are thirstier than the 3.0l
Had one at reef level. It had no power or torque for that heavy body and got rid of it after 1year. Bought a 3.0d model afterwards and have been ecstatic over it since. Will never consider a petrol SUV ever again, utter garbage.