The Get Rich Quick Club by Dan Gutman

We, the members of the Get Rich Quick Club, in order to form a more perfect summer, vow that we will figure out a way to make a million dollars by September. We agree that neither rain nor snow nor gloom of night will prevent us from achieving our stated goal, till death do us part.

Gina Tumolo and her Get Rich Quick Club are determined to make their summer pay off. They're going to make a pact and hatch a scheme, and their small-town life will never be the same again.