For that kind of mileage, I'd be taking inspiration from taxi drivers. A diesel Toyota Avensis would be very robust and your budget will get you one with lots of life left in it. It's not an exciting or interesting car, but it will do the job and ought to be comfortable. You can get an estate version for carrying the dog, too. If you bought a 2011 model with around 70,000 miles on the clock, I'd look to keep it for three or four years before seeking a replacement. As an alternative, the Skoda Superb is a bit more comfortable and spacious than the Avensis. We've not had many reports of issues with the diesel engines, although the DSG automatic gearboxes can be troublesome.