The Five Dollar Bill is the only money that you can get in the island. Yeah, you will surely beat the island and may get the $1,000,000, but there will be a twist in the end (but don’t be disappointed, it’s not going to be bad). With this, you can only afford to buy a Sports Drink in the General store, which is what you need actually to continue and get some other items to complete the island quest.
How to Get the Five Dollar Bill
Go to the right side of the Main Street till you find a tree, there you can see a five dollar bill hanging on its branch, maybe the wind blew it for you to find. So jump over the tree and take the money.