Story highlights National September 11 Memorial Museum will charge admission

The admission charge will range from $20 to $25, memorial spokesman says

The fee "is taking advantage of tourists," victims families' advocate says

If the fee is necessary, "they need to do it," surviving husband says

Some families of 9/11 victims are outraged over the National September 11 Memorial Museum's decision to charge admission for visitors.

Sally Regenhard, assistant chairwoman of the group 9/11 Parents and Families of Firefighters and WTC Victims, called the fee a "slap in the face" on Sunday.

"Patriotic people from all corners of the country go to teach their children something and show respect, and now they will be faced with this fee? It is outrageous," she said.

"This feeds the idea of New York City being money-hungry. It is taking advantage of tourists," Regenhard said. "Making people pay to grieve is going to prevent people from paying their respects and learn about the victims."

9/11 Memorial communications manager Anthony Guido said that an exact price has not yet been set, but it will range from $20 to $25. Family members of 9/11 victims are exempt from all memorial-museum fees and charges, Guido said. The museum will open in 2014.

According to Guido, 9/11 museum officials looked to other institutions in the country for guidance on admission charges, such as the Oklahoma City National Memorial & Museum, which charges $12 for adults.

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The memorial-museum declined to comment on Regenhard's statements.

But not all family members of 9/11 victims agree with Regenhard.

Charles Wolf told CNN affiliate WCBS: "I think if it's necessary, they need to do it, because I want this museum to be good. We've taken a horrible, horrible disaster -- in which my wife was lost -- and we're making it better."