The things to check on most Mondeos is rust in the rear arches, Heater controls ie the direction to Screen, feet etc & rear door locks. They can also get through Lower arms. The old ST24's & 200 as mentioned can suffer from Water pump failures. You can get the metal impellor ones for £30 from most motor parts stores.

Great cars for the money but I'd go for the 24 & save yourself a load of cash.