The straight six 3.5 litre engines from the 1988-1992 aE34s are incredibly reliable, not to mention powerful (the M30 engines). THe V8 engines that replaced them are known for being average - generally don't achieve the same mileage, and the performance is not significant improved.
Heres some cheapies currently on trade me: red535i
This one presumably is the M20 engine, but still a nice car
red525i
And a very nice one here:
535i
What about this 5 series/8 series hybrid?!
beauty or beast?