Cost of owning a mini diesel?

Hi, I'm thinking of buying a 2007 -2009 mini cooper diesel. I'm interested in finding out the running costs of a mini diesel before I buy one .e.g. how much mileage you get out of a fuel of tank and costs, and especially servicing costs, etc.
Also if anyone knows of any 2007- 2009 mini cooper diesel's for sale with low mileage (up to 40,000) please let me know. Thanks, Rachael