LEWISTON – A proposed replacement for Farwell Elementary School is proving more expensive than first planned because of rising construction costs, a recent property purchase agreement and a new plan that makes the school bigger.

The $10 million project could now cost up to $11.3 million.

The original plan called for the 50-year-old school to be torn down and replaced with a new facility on the same 4.6-acre site. The school serves 320 pupils in kindergarten through grade six. Its 50,000-square-foot replacement was expected to accommodate about 400.

Now, Department of Education officials have agreed to a 53,125-square-foot replacement that can accommodate 425 students. Owners of 112 Farwell St. have agreed to sell the abutting property, giving the new school an additional quarter-acre for green space and separate dropoff areas for school buses and parents driving their kids to school.

“It enhances the project immensely,” said Superintendent Leon Levesque.

The school department has signed an option agreement with 112 Farwell St. owners Robert and Pat Reny. The property’s negotiating price has not been disclosed. The city’s Web site lists the property value at $62,200.

The new site will go to the State Board of Education for approval Tuesday.

Because of the larger building, the extra land and skyrocketing construction costs, Department of Education officials agreed to raise the project’s price limit. The new price tag will go to the state board, whose approval is required, for consideration on Oct. 13.

Lewiston will hold a public meeting on the new plan at 6:30 p.m. Tuesday, Sept. 21, at Farwell Elementary School. Officials will likely take a third straw vote then, Levesque said.

Under the current school funding formula, the state is expected to pay 47 percent of the new school’s cost. The city would pay 53 percent.

When the state’s new funding formula, called Essential Programs and Services, begins next year, the state’s share will likely be higher, Levesque said.

The school department would also like to build a 3,395-square-foot gymnasium in the new school. Because the bigger gym would be an extra expense, the city would have to pay the $597,000 for it without state help.

The Farwell project could go to a referendum vote in Lewiston as early as December.