If paying for the Focus is possible, I would go with that. In that case, you will at least know what your car payments will be each month. It doesn't take much for repairs on the Contour to exceed what it would cost for you to have the Focus each month.
Focus: Peace of mind.
Contour: Never know what could happen.
If you passed on the Focus and your tranny blew next week, you would really be wishing you went with the Focus. I can't say there's as positive a thought about keeping the Contour, other than hoping/thinking/wishing that it goes a couple more years, months even, without major repairs needed.