Money or the lack of it was not the only cause of the French Revolution. It was one of the causes that eventually lead to the Revolution.
One cause that led to the revolution was the peasants. They were getting tired of being heavily taxed by the monarch and the nobility and also the church. Taxation was too chaotic and complicated especially when goods traveled to other regions of France.
The main burdens of the taxation were borne by the classes least able to support which was basically most of the peasants. Also due to a poor harvest season in 1788, the price of bread and many other foods went up by 50% .This made them even more desperate.
Another cause was that the king who was desperate for money couldn't tax the nobility. Most of the revenue-gathering land was in the hands of the aristocracy who were exempt from taxation.
The aristocracy were getting richer while the king was getting poorer.
Another cause of the French revolution was the fact that the 3rd Estate broke away from the Estates-general and proclaimed itself the 'National Assembly'. They represented the workers and also were influenced by a very influential group of French philosophers. Out came new ideas of what a society should be and how it should be run. There was increasing demand of liberation from the tyranny of aristocracy, from the Church and the restrictions of the feudal system. People began to believe in these ideas.
Another cause was that the Etats-Generaux (States-general), the assembly of the 3 estates did nothing. They were supposed to represent the whole realm but this only existed as a memory since the last time they were called upon was in 1614.
All these causes eventually led to what we call the French revolution.