Every day in your town there is one specific rock that you can hit and when you hit that specific rock it will spit out money and you have a certain time limit, so hit it fast!!!! Something that always helps me hit it is: before you test it to be the "Money Rock" you dig holes with your shovel (what you hit the money rock with) around yourself so when you hit the rock, it can't push you backwards, waste your time and give you less money.
P.S. these are the amounts of money you can get: 100 bells, 200 bells, 300 bells,
500 bells,1,000 bells, 2,000 bells, and not very often but 5,000 bells.