Gonna rock the boat here. I totally agree with the suggestions of A series 2.8 TDi and 2.5 TDS. Cracking motors and I prefer the older shape to the B Series. However shall we look further afield but not as far from home as a Mitsubishi or Toyota. Back to grass roots we go and look at Isuzu

The Trooper is what your beloved Vauxhalls are based on and to be honest just as cheap to buy/maintain. The Mk.II and Mk.III both sport the 3.1 TD which has the poke and torque of the 2.8 (as its the same engine just bigger bore or stroke cannot remember which one) to deal with the increased weight. The Mk.III had a few refinements on it with a curvier dash and a little more grunt to boot. The one to possibly avoid was the import (Bighorn) Mk.III (read post 1995) automatics as they had an electric fuel pump. Not unreliable just harder to get spares for the fuel pump. If you want to drain your wallet each month you could plump for the 3.2 V6 (as found in the Frontera Series B).
Now I wouldn't of suggested this 6 months ago but I think its also a plausible option now. The Mk.IV 3.0 had a horrendous issue with injector sleeves. The common rail on the injector line (bearing in mind this is a Caterpillar design) would leak diesel ino the oil supply causing damage to the engine as a whole. Now Isuzu did a stealth recal on all 3.0 engines and still offer it. Have heard stories of entire engines being replaced at dealer expense over this. They have resolved the issue and I truely believe that its near enough resolved with the ones needing the work to be done and the new ones not needing the work. If you do think of buying one then you can phone Isuzu with the VIN number and they can tell you if the recall work needs doing or not. Either way the 3.0 TD is a 160bhp, 245lb-ft 30mpg 4x4.