I put in some numbers into the cost of these mini vehicles from new to 30k miles, and new to 100k miles. Of course, this does not include oil changes, and other services. These costs are SOLELY using the MSRP (U.S.) before any fees or extra costs, and using fuel price of 3.50 per U.S. gallon, other than the Cooper which needs premium, and I priced at 3.75.
I used information found here: 2-15 Micra vs competitors, power to weight ratio comparison
And replaced information if I found differences on the website. MINI data was also collected from FuelEconomy.gov.
Reviewing this, bar any errors on my part, the Micra is the best bet at 100k miles.