50 Cent was reportedly spending $70,000 a month on his 52-room Connecticut home. We asked 3 realtors to break down the 'invisible' costs of owning a mansion.

Katie Warren/Business Insider

A house in Westchester County, New York.

• 50 Cent recently sold a $2.9 million Connecticut mansion that was reportedly costing him $70,000 per month to keep.
• Such large estates can carry "invisible" costs that quickly add up to tens of thousands of dollars, according to real-estate agents.
• Costs that might not be obvious include New York's "mansion tax," sky-high utility bills, landscaping, maintenance emergencies, security systems, and smart home technology.
• One of the biggest expenses can be smart home technology, which has to be updated every few months and costs up to $20,000 per update, according to one Douglas Elliman broker.
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A massive mansion with perfectly manicured grounds, a private pool, and a high-tech security system may sound like a dream home to many.

But such a house will cost you much more than just the mortgage.

"There are many 'invisible costs' of owning a so-called mansion," RC Atlee of Compass, who sells luxury homes in the Hamptons, told Business Insider.

These costs, which can include utility bills, landscaping, maintenance emergencies, security systems, and smart home technology, can quickly add up to thousands of dollars per month.

Take 50 Cent, who recently sold his 52-room Connecticut mansion for $2.9 million after 12 years. The rapper was reportedly spending about $70,000 per month - including property taxes and mortgage payments - to keep the house, which he bought for $4.1 million in 2003. The 50,000-square-foot home includes two private pools and indoor and outdoor basketball courts.

Read more: 50 Cent's Connecticut mansion, once listed for $18.5 million, has finally sold at an 84% discount after 12 years. Here's what the 52-room house looks like.

Atlee pointed to New York's "mansion tax," which requires anyone buying a residential property for more than $1 million to pay 1% of the sale price. The tax can be up to 4.15% of a property selling for $25 million or more, he said.

"Things like that are a part of our standard disclaimer and should always be communicated to the buyer," Atlee said.

But taxes are just the beginning.

The invisible costs of owning a mansion can add up

Homeowners expect to pay utility bills, of course, but what some buyers may not know is how much these costs can add up in a large home - especially when they're coming from an apartment in the city.

"In a condo, your heat and hot water is probably part of your common charges, but if you buy say, a townhouse with 14-foot ceilings and have to pay all of your own utilities including heat, it can cost $2,000 to 3,000 per month," Justin Rubinstein of the Michael Graves Team at Compass told Business Insider.

And then there's landscaping. Keeping lawns, gardens, and water features in pristine condition can cost thousands per month depending on the size of the home.

Douglas Elliman

50 Cent's former home in Farmington, Connecticut.

"Landscaping is always important, because who wants to spend $10 million on a house and have an unappealing façade or front yard?" Rubinstein said. "Depending on the size of the property, this can easily eclipse $100,000 per year."

Rubinstein says homeowners should also consider setting aside money each month for maintenance emergencies.

"Eventually, there will be a flood, or an electrical issue, or a roof repair," he said. "And whether you save money each month for that, or you just risk it and wait for something to happen, it's definitely an invisible cost."

Smart home systems may be the 'biggest hidden cost'

Jennifer Leahy of Douglas Elliman, who sells homes between $500,000 and $9 million in affluent Fairfield County, Connecticut, said larger houses in Fairfield - those around 12,000 square feet or larger - can cost homeowners an average of $10,000 per month in upkeep, from utilities to landscaping to smart home systems.

Read more: I spent a day in one of America's richest cities, a town an hour from New York City where hedge fund managers live in multimillion-dollar homes. It was immediately clear why it's a haven for Wall Street types.

"I think probably the biggest hidden cost is that smart home systems, like a Crestron, must be updated with frequency and the updates can cost - no joke - $20,000 a pop," Leahy told Business Insider. "And my clients sometimes have to update them every three to six months."

And don't forget about home security.

Leahy said many of the homes she sells have home security systems from Brosnan Security, a company that deals with many of the major estates in Greenwich, Connecticut, where the average home price is $3 million, according to Leahy.

"To have video monitoring, surveillance, drones that descend when people come on the property - that could cost thousands of dollars," she said.

Still, $70,000 per month - what 50 Cent was reportedly paying - is not the norm, even in ritzy Greenwich, Leahy said. Even the larger homes in town are only around 12,000 square feet, she says, four times smaller than 50 Cent's former home, she said. But for size of the rapper's former home, $70,000 per month doesn't surprise her.

Owning a mansion like that, Leahy says, is like "having a small hotel."