I think using money is too literal and specific and because of this the suggestions so far do not shout out "REWARD" when first viewed but rather savings or something to do with a bank.
I live in the UK and there are many generic reward schemes but one of the most prevalent is Nectar (Nectar is a sweet reward for bees). 30 years ago people in the UK when they saw the word Nectar would probably not associate it with a reward of any kind, but now, i would hazard a guess that a very large slice of the population would and that is from brand recognition and extensive marketing.
I guess, what I'm saying is you don't need to go straight to the money analogies, you can pick something more abstract. How about a Carrot? The Carrot and the stick story has been knocking around for a while? Does the donkey get the carrot as a reward or the stick as punishment? I think its well known enough that you could perhaps use it.
"You've collected 50 Golden Carrots! Redeem"
You could even have a play on words like Carat as in the unit of mass used to measure the purity of gold.
I'm not suggesting you run with the Carrot idea, its just an "outside the box" thinking exercise and I hope gets you away from literal analogies.