I have a 325D Saloon (E90 version) 2007. I presume it’s the same 200bhp engine.
Cost to fill up when at maybe quarter tank is approx £65.00 on today’s fuel prices.
On a long motorway journey at 70 / 75 mph I can get 49mpg. 45mpg at 90mph (on a private airfield of course).
Round town, nothing special, maybe 36mpg tops.
In total I get around 400 miles per tank, i mainly do town driving with a small amount of motorway. Obviously goes further with a steady motorway journey. let me know if you want any further info.
Happy motoring!!