It's sort of like buying a £4000 i7 Quad Core, 16GB RAM, 4 x SSD's, nVidia GTX 690 then insist on using a 15" CRT Beko screen because you don't want spend more than £50 on the monitor.
It just...doesn't make sense and ruins the whole thing?
Why don't you set your budget at something like £16k and use this to allow you to buy a car with an engine that compliments it, rather than ruins it. Best of both worlds no?
I have a 3 Series coupe and it is a fantastic car, however the 320d is just souless. And, i swear to you, if i had spent £18000 on a 320d, i would be crying into my cornflakes, when i could have spent a bit less and had an engine which is silky smooth, quiet AND economical at the same time.