First figure out what's wrong with the motor. If BMW quoted R70k to fix it sounds like the motor rolled bearings and that the bottom of the motor needs a rebuild (crank and bearings)
The clutch replacement on that car was R45k, that's a big chunk of maintenance that won't be needed. If you play your cards right, you can have a real nice M3 for R300k my man, provided it's cosmetically perfect.