Bonanza could be as bad as 1200ft, I guess, for a safe turnback. The RAF include turnback in the pre-takeoff brief, with a specified altitude. I seem to recall (it's been a few years) that the Tutor for example is briefed as 'If the engine fails below 600ft I will land straight ahead. If the engine fails above 600ft I will consider turning back to the airfield to land.'
Note 'consider' i.e. it's a judgment call.
Tim