It sounds like your repair costs have been pretty reasonable so far, a 940 will likely be cheaper just because it'll be much newer and have less wear and deterioration, but in the long run if your 240 is in relatively good shape it might not save you much. Personally I'd say it's a tossup and/or depends on too many different things. If you can do some of the work yourself either car can be kept running almost indefinitly rather easily, if you have to pay someone else to do it, both are comparable to work on with some things being easier on one and some easier on the other.