Rhode Island is one of 18 states building its own marketplace, which is designed to help individuals and small businesses shop for insurance plans. Most Americans will be required to have coverage as of Jan. 1, and many will be able to access federal subsidies through the exchange.

Ferguson told the legislative panel that HealthSource RI's customer service center will open on Monday and that an advertising campaign will begin on Oct. 1.

She said significant work is already being done to reach out to populations state officials hope will get coverage through the exchange as well as an expansion of Medicaid. Rhode Island is putting a big focus on the state's 30,000 small businesses, about half of which offer coverage now.

About 124,000 people are currently uninsured in Rhode Island in a population of just over 1 million.

Ferguson noted there are still many unknowns about the exchange, including how many people will enroll and how much it will ultimately cost the state to run.

"This is brand new — never been done," she told lawmakers.

While the exchange is being built with more than $80 million in federal money, the state will have to fund it starting in 2015. Ferguson said it could cost Rhode Island between $17.9 million and $23.9 million a year to do so.

Finance Chairman Helio Melo, D-East Providence, expressed frustration that she couldn't be more specific.

"We are just trying to figure out how this is going to work," he said. "We don't know if we're building a colonial, a mansion, a bungalow. It always seems like we'll continue with construction (and) we'll worry about how much it's going to cost us later."

Three carriers are participating in HealthSource RI next year; 12 individual and 16 small group plans will be available. Two more insurers are expected to join the exchange the following year, Ferguson said.