A BMW X3 is not an inexpensive vehicle to repair and maintain. At the age and mileage of the vehicle you are considering, it would not be surprising to spend $2000 or more in a typical year for maintenance and repairs. If something major goes wrong with the engine, transmission or xDrive, repairs may cost much more.
Edmunds True Cost to Own estimates appear high in my opinion, but provide additional data to consider in your deliberations.
https://www.edmunds.com/bmw/x3/2013/...3/cost-to-own/