Sorry to hear that
In my experience diesels are always more economical than petrols, but I wouldn't recommend one with a DPF for short journeys. We've got an X5 3.0d that the woman uses for her dog-walking business so it's always doing door-to-door trips and averages about 30mpg. By comparison she used to have a petrol Honda HRV 1.6 which averaged high 20s for the same driving. Admittedly the cost saving may be negligible if you're not doing many miles.
I dabbled with a Saab 9-5 3.0 Tid before I bought my E46 and it was a great car other than the engine dropping a liner. Those engines are notorious so avoid that one.