How about no rewards whatsoever?

The exam season is upon us and I have been mulling over the merits and disadvantages of bribing, sorry I mean rewarding, children in a bid to make them get down to studying.
Several parents have been talking about the right way forward to try to push, sorry I mean motivate, their youngsters into the correct approach to exams.
Some children are clearly highly self-motivated, so they're a doddle when it comes to exams.  Looking back to my schooldays, I can see that I fell into this category because the academic arena was the only arena in which I had a hope of shining.  
But what about those children whose minds aren't solely fixed on getting the top marks in the French paper?  Should you offer a reward as an incentive, and if you do, should the reward be granted for effort or for attainment?
I can remember some youngsters being promised £5 for each O-level they passed when I was sitting my exams.  My parents never offered me anything - I just got on and did it anyway - but I privately disagreed that my peers should get a monetary reward.   My scruples were very high at that point in my life.
One and only son is in his early years at secondary school, so he won't be facing any ''really important life-changing'' examinations.   But the reward question has cropped up.  I nag him to do his homework and help out lots when it comes to revision.  I know, I know, you are all saying he has to learn to do it himself and become an independent learner - I might take that approach next year.  He has asked for a BlackBerry in return for doing well in his forthcoming exams.   My gob dropped open to my knees, and then dropped even further when I learned the husband had sort of agreed to it.  
''How about you put the effort in because it would be a good idea all round for your future schooling and employment prospects?'' I said, tersely.  ''Not because you are going to be rewarded.''
''I'll put some of the money in myself,'' he replied.  ''I've been saving my pocket money.''
This floored me.
Privately, I later said to the husband the bribes would have to go up each year.
''What are you going to offer him when he does his GCSEs? '' I asked. ''A flamin' car.''
The husband acknowledged I had a point. 
I had a wicked thought - usually I reward effort by buying a book or a meal out and make sure it's something not over the top.  But this year maybe I should only reward for attainment despite genuinely thinking effort is more important when it comes to life skills and the world of work.   What to do?