From time to time (full driving cars) 323i-m52tu. 320i-m54b22. Pop up for around 500-600e.
If you break the car you could have the conversion standing you under 250e depending on alloys and leather that comes with the car.

What's involved.
Engine, box, loom out in one lump. Also ecu and ews out.
Swap over exhausts.
It's straight forward. Id sway 2 men max 2-2.5 days on the ground.