The 9/11 Memorial Museum opens to the public this week, but the journey to its unveiling has not been without controversy. Questions over the purpose of the museum have been well-reported, but recent concerns have been raised over the relatively high cost of admission.

Those wishing to visit the memorial will have to pay a $24 admission fee.

At a recent press conference, former Mayor Michael Bloomberg said that those upset by the high cost should write to Congress. His point? While the U.S. government has provided $250 million towards the contruction of the 9/11 Memorial, more financial resources are needed to maintain security and its high operating costs.

Federal and state support are issues that factor into the price of admission at other memorials in the U.S. and around the world.

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The Oklahoma City National Memorial, for example, does not receive any federal funding to contribute to the cost of its annual operation. Though, like the 9/11 Memorial, the museum did receive funding for the initial construction costs. Along with the $10 entrance fee paid by visitors, the self-sustaining museum covers its expenses using “store sales, the OKC Memorial Marathon, [and] earnings from an endowment and private fundraising.”

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The Anne Frank House in Amsterdam also charges an admission fee — a practice it began in the early 1970s when the Anne Frank Foundation began having diffuclty shouldering the costs of maintaining the house. Revenue from visitors to the museum now covers 95 percent of the organization’s annual budget. While it does receive funding from the EU and the Dutch government, the money is reserved exclusively for projects not involved in running the museum.

Back in the U.S, while legislation was introduced in 2011 to set up a regular subsidy for the 9/11 Memorial, it was basically shelved. It would seem that for now, the price of admission remains.