1.4/1.6 Mk 6/7 Fiestas do according to autotrader.
Mk7 does ~55mpg real world: https://www.honestjohn.co.uk/realmpg/ford/fiesta-2008
Mk6 does ~56mpg real world: https://www.honestjohn.co.uk/realmpg/ford/fiesta-2002
So the saving will probably be about half what you calculated. I'm still unconvinced that you are doing sufficient mileage to justify it, bearing in mind you'd be buying a 10 year old turbodiesel with unknown history to replace a car that by your own admission is incredibly cheap to run. It would probably take you a couple of years just to break even and then all it would take would be a busted clutch or whatever to burn up the next few years of saving (assuming that you will still be doing the same mileage once you graduate).


