e28 mounts are definitely a cheaper route. Expect some added in cabin noise and vibration.
I went to IE on a sat and picked up a pair of poly eurathane mounts for $80. Engine still isnt in the car yet so i cant tell you what they feel like.
i duno if this was mentioned yet but the e21 engine mounts work, and theryre less then 50-100$ (the 5 serries ones i believe) call patric and BMA, he'll hook you up.