TRENTON -- Gov. Chris Christie's planned $300 million renovation of the Statehouse could cost as much as $750 million in the long run, according to figures the treasurer provided the Assembly Budget Committee on Wednesday.

The modernization of the executive offices of the 224-year-old Statehouse will be financed through the Economic Development Agency in an arrangement some Democratic lawmakers have argued is designed to evade legislative and voter approval.

The planned renovation is expected to cost about $287 million, including contingencies, but as with any construction project, the price tag swells when the cost of borrowing is wrapped in.

"As with any capital financing, which is appropriate for long-term capital projects, you're going to have a principal payment and an interest payment," Treasurer Ford Scudder told the committee.

While the debt would belong to the EDA, the state Legislature would have to appropriate those funds every year to pay it down.

Scudder offered only loose estimates, saying it may cost the state $20 million to $25 million a year for 20 to 30 years to cover both principal and interest. That's a range of a range of $400 million to $750 million -- a sliver of the more than $35 billion annual budget.

A spokesman for the Treasury Department, Willem Rijksen, said later that those are "rough estimates -- not hard numbers. Obviously, the precise costs won't be determined until financing is finalized."

An eight-person State Capitol Joint Management Commission, comprised of top staffers from Christie's administration and from the offices of Assembly and Senate Democrats and Republicans, approved the massive renovation last month.

Executive branch spaces under Trenton's golden dome have not been updated since the 1950s, save for emergency repairs, and a design consultant declared the executive offices in "a state of advanced deterioration that threatens the life, health and safety" of everyone who works there.

The executive branch occupies a near block-long section of the building that faces West State Street and houses the offices of the governor, treasurer, secretary of state, their staffs and the press corps.

The full renovation is expected to take four years, dislocating executive branch employees and the future governor to offices owned or leased by the state elsewhere on the block.

Under the financing scheme, the joint commission will for $1 lease the historic building to the EDA, which will sublease it back to the commission, which will reimburse the EDA in the form of rent payments.

Scudder called it a "standard financing" arrangement when questioned by Assemblyman John Burzichelli (D-Gloucester), who accused the administration of routing it through the EDA to circumvent voter and legislative participation.

Scudder said that as the renovation and upkeep of state office buildings and the Statehouse complex is "central to the economic development of the capital city," the project falls within the scope of the EDA's charge.

The treasurer's office found the lease deal would be the "most appropriate and least expensive," he said.

Rijksen, the Treasury Department spokesman, confirmed the bond sale will not require voter approval, despite a constitutional amendment giving voters a say in state debt.

The EDA's statutory authority, he said, predates that so-called Lance Amendment -- named after U.S. Rep. Leonard Lance (R-7th Dist.) during his time in the state Senate.

Samantha Marcus may be reached at smarcus@njadvancemedia.com. Follow her on Twitter @samanthamarcus. Find NJ.com Politics on Facebook.