To the original poster, I think it depends on what standard you want to set for your kid.

In my family A’s were expected not rewarded. It’s the same sort of pyschology but without the cash prize.

Not every kid (cash / no cash) will be able to get A’s all the time. I think it is more about setting their work ethic for the rest of their lives.

Personally, I would be worried that your kid would then expect a bribe / incentive to perform later on in life. My experience is that life will kick you in the shins with that attitude….unless you are a CA homeowner who bought too much house.