£800 is 2nd banger territory. But if you can find a 1997-1999 Mondeo 1.8LX or 2.0LX that hasn't been scrapped, that is the most reliable car according to Warranty Direct statistics. The trouble is, if the clutch fails, it will cost as much to replace as the car is worth, so check that very carefully. A Mondeo 2.0LX run on Shell V-Power will do 40mpg on a long run. Used for repeated short runs from cold this will of course drop below 30mpg.