TD5 or 4 ive had both and the biz
They dont do a Discovery with a TD4 mate, they were in the Freelanders. Doing 500 miles a week whatever 4x4 you get in your price range is not going to be cheap on the wallet with fuel..... Unless you go down this route, I would get a defender, convert it to run on veg oil then start asking around your local chip shops and restrants for their old oil!! Fuel cost then would be £0