HDi fun
TC ModFather
You, my friend, have a low perception of ambitions. Easily (but not necessarily cheaply) achieved on many many 4 cylinder motors.
That's kind of what I was getting at, I think. Not many fours are engineered to stand that much torque.
It can, of course, be done, but it'll likely cost a few quid (as you say) to get everything else to stand up to the angular forces involved. Which, basically means that we agree - it's a cost thing.