Cuba is not an inexpensive destination as one might imagine. We recommend that you bring as much money (in cash) as you would for any other trip of the same duration. As a general guideline, a minimum of $100 per day is recommended for incidentals and of course if you are thinking about purchasing artwork, or other types of souvenirs, you may want to bring more. There is not a lot to buy in Cuba but any items that are available tend to be expensive or comparable with prices in the U.S.
It is important to remember that Cuba is still a cash economy and there are very few if any places where you will be able to use your credit card or debit card. Credit cards should be if you run out of cash during your trip.
Securely carrying your funds in a money belt and leaving excess funds behind in your hotel safe is also a good idea.