Rent one for £350 a month.
There is no way on earth I would buy a new 3 series unless I was doing 30k miles a year and was planning on keeping it for at least 4 or 5 years.
320d Sport auto with business media on contract hire is around £360 a month with a £1000 deposit.
http://www.contracthireandleasing.co...ries/11609558/
So over 2 years will cost you £9000, over 3 years will be around £13k, there is no way a £39k 320d will loose that little over the same period if you are buying cash, and I bet the figures if using finance are 3 to 4 times the deposit and then 50% more each month, and you will still just hand the keys back at the end.