All of these carriers are paying attractions. You have to buy a ticket to get into see them and they all run activities within the museum to make more money. They all have numerous attractions and attempt to operate at least on a break even basis, but are really meant to make a profit for their investors if they can. They have to show that they can cover all the costs (for the carrier setup, the maintenance, the people working there, the utilities, land, etc.) before the Navy approves the final deal.How much does it cost to turn aircraft carrier into museum ? Non-profit self-sustained NGO would have a hard time to pull it of in these economic conditions without government help .
On the other hand , you could try to do something like Chinese have done to Kiev , turn ship into hotel and theme park on commercial basis . It may not be pure and dignified as museum , but at least you would preserve something and avoid scrapping .
So, they take donations, they take investments, they charge to get in, they have items they sell, they sell refreshments, they hold New Year's Eve parties,etc., etc. to raise the initial funds and then keep the money coming in so they are not going under financially.
As to the initial cost, depending on the condition of the vessel, it can cost many millions of dollars to get started.
It's a pretty well defined process. In addition to these five carriers, there are maybe ten or more large battleships, a few cruisers and many destroyers and submarines that are operated in this fashion all over the country. They pretty much know what they have to do and if they can clear the initial hurdle of getting started, the vast majority of them then go on to operate for many, many years.