If Concord buys a former insurance building to become a future police station, an idea that will be discussed by the city council Monday night, the $4 million purchase would only be the start of costs.

Concord’s capital improvements program includes an estimate of $27.5 million over the coming years to design and establish a modern police station.

Although this estimate is not specifically tied to buying and upgrading the Concord Group building, it shows the magnitude of costs that would be involved in meeting the unique needs of a police station such as holding cells, a sally port and strict security.

Concord isn’t unique in facing such costs. Bedford, for example, is talking about spending $36.5 million to build a police and fire complex on land it bought two years ago. Even staying at Green Street would be expensive: A 2021 study estimated it would cost $10.5 million and take three years to expand and renovate the current police station.

The green office building on Bouton Street facing North State Street held the Concord Group Insurance for more than half a century until that firm shifted to Bedford this year as part of an increased focus on the Massachusetts market. City staff have recommended purchasing it from developer Steve Duprey for $4.09 million. The council will consider that idea at their regular meeting on Monday.

Duprey’s firm has an agreement to purchase the property from the Concord Group for $3.5 million. The Concord Group leases city property from the Duprey Co. and the sale price reflects negotiations to terminate those leases.

The city’s 2021 study said a police station should be 27,700 square feet, some 6,000 more than the current station. The Concord Group building is much bigger, about 38,000 square feet, creating the possibility of other city services based out of the facility.

A November report from Deputy City Manager Matt Walsh said the administration would explore “including space for the Prosecutor’s Office in the new Police Headquarters,” which would save about $41,000 annually in rental costs.

The building has 113 parking spaces, compared to the 37 allocated to the police at the Green Street station. It has three separate driveways, which can be valuable for emergency services.

If the council agrees to go ahead and buy the Concord Group building, the purchase probably wouldn’t be completed until next summer, with any upgrades or construction coming after that.