(CNN) Eight prototypes bidding to become the model for President Donald Trump's proposed border wall cost between $300,000 and $500,000 each to build -- with the Department of Homeland security footing the bill.

But since construction of the prototypes began in September, 2017, the taxpayers of San Diego have paid about $2.3 million to protect them.

According to the San Diego Police Department and San Diego Sheriff's Department, the two local agencies have been helping to provide security around the structures. The majority of the $2.3 million was spent during the one-month construction phase from September 26 to October 26 of 2017. During that construction phase, 298 sheriff's deputies were provided for security duties.

"We're not there to protect the walls, we're there to protect the people," said Lt . Karen Stubkjaer of the San Diego Sheriff's Department. "We are providing life and safety protection to those who might come to protest and view the prototypes."

The eight prototypes were chosen by Customs and Border Protection to be built along the border in Otay Mesa, near San Diego.

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