There is no actual "visa." You purchase a tourist card, either upon arrival in Cuba, or from the airline when you check in for your flight there.

But I think you’re asking the wrong questions. The bigger issue is not what Cuba requires but rather what the U.S. allows us Americans to do, and that's a lot more complicated. The trip as you describe would not conform to U.S. law. Officially, we cannot visit Cuba as independent tourists. We are allowed to go with organized groups on what is called a "people-to-people" tour whose focus is cultural exchange. We can also go on family visits, humanitarian visits, journalism projects, ... There are 12 permitted categories, but routine tourism is not one of them.

What you choose to do is your own concern. If you go on the trip you're describing, you'd have to travel via a third country. A charter flight between the U.S. and Cuba is not be an option for you unless you travel under one of the 12 approved categories.