Smaller CARS get better economy. In my experience of having different company cars, the engine size has very little bearing on the fuel economy. Factors I've found that make a difference.
Weight of the car
Gearing at high speeds
Generally big cars with small engines (407 1.6 HDI, Laguna 1.5 dCi, Corolla 1.4 D-4D etc) will do good enough fuel economy at 55mph, which is about the speed they're doing when tested for emissions figures etc, but get them above this speed to 75mph and the economy drops drastically. even if they have a 6th gear fitted, the engine is under pressure going up hills and overtaking.
I found this on autotrader, 2003 Avensis 2.0 D-4D with 40,000 miles, these are phenomonal on juice, and nippy too. this one has satnav and aircon.
would work out at €5065 plus travel costs.
Granted it's not as modern as a 307 (A lot of the design being based on the Carina E) but I reckon it's better than anything else for the money.
AD HERE