X3 buying experience in UK?

Hi,
After giving it a lot of thought, I’ve decided not to go for the X1 because of the limited space. Our stroller is quite large, so I think the extra room in the X3 would be a better fit.
What model year would you recommend for an X3, and what would you consider a fair price to pay? Also, do you think it’s worth buying a BMW Approved Used car, or are their prices generally too inflated?