I 100% agree with don't buy a diseasall,,its the fuel of satan and should only be used for cleaning engine parts
but if you must get a derv generator powered vehicle you could try and get Toyota Yaris 1.4D taty ones come up around 500 notes
and in the theme of the ford Punny my son has done the 1.7 into mk5 fiesta's 4 times now,
he gets the donor puma for 80>150 and the fiesta (zetec s with the famous blown motor) for 100>150
and the swap is easy peasy, the puma chassis even though based on the fester comes out at over 900 kgs (950 maybe)
the fiesta's are 850 ish so makes a quicker and more practical car than the cramped puma
the weights are based on weighing the shells in etc so are approx
but the end result is they recon is a lot better than a lightly tweaked/stripped out punny