Hi
Of your selections the cheapest to run will be the Focus. It is reliable and parts are well priced. Next will be the Golf because it is very reliable, but parts are not so cheap. The Rover's reliability is less good and being a bigger car than the others will be more expensive to run one way or another.
On this budget you will be looking at buying a 80,000 miles 1.4 Focus at an auction or from a private seller in a rush. You can expect 40-43 mpg, which is 5.47 per 100 Km. Our free buyers guide lists 30 things to check before buying to ensure there are no common faults or potential problems.