Upkeep on the x5 is the key.

Buying an older x5 with more mileage might actually be cheaper than one with lower mileage if the older one is current on service schedules.

At 70-80K miles, I would expect some suspension items to need repair
CV boots
control arms


If you want to go cheap and will keep the car a long time, I would get a x5 with a stick shift. why?
- low purchase price
- sidesteps issues with the automatic transmission
- more fun to drive