On Boylston Street, the last of the businesses closed by the marathon bombings will be up and running Saturday night. They've been out of business for more than 10 days, at huge expense. Many will not get any insurance money if the federal government officially declares the bombings an act of terrorism.

On Thursday and Friday, business was bustling at Marathon Sports, right at the marathon finish line. People were buying running gear and making donations to the victims. It was right out front last week that the first of the two bombs exploded. Owner Colin Peddie saw his store turn into a crime scene.

"The last thing on my mind was the cost of business," Peddi said. "Not until today have I thought about the commerce side of things."

But the commerce side is big. Marathon Sports was closed for more than a week –- a major one at that.

"It's been significant. The four/five days after the marathon are in the top ten business days of the year for us," Peddie explained.

But at least Peddie’s inventory didn’t go bad. That’s what happened at Abe & Louie's, a steakhouse by the second explosion. Manager Tim Fannin said everything had to go.

"You know, I've opened a few new restaurants, and this is as close as it feels to it, with a bunch of whirring of refrigerators, and you don’t see any food around," Fannin said.

Businesses tend to buy insurance for unplanned events like this. But after 9/11, Congress passed a law to exclude terrorism from the standard business interruption insurance contract. You have to pay extra. And most small companies don’t. That means if the federal government officially declares the bombings terrorism, many business are going to be on the hook.

Meg Mainzer-Cohen is the head of The Back Bay Association representing area businesses. She’s been working with the city and state regulators to twist the arms of insurance companies to be generous, even if the damages are not supposed to be covered.

"The costs associated with having a business continued, but the revenue was eliminated," Mainzer-Cohen explained. "It is my goal to let no business close because of this situation."

But why should insurance companies pay when it’s not their responsibility, asks Bob Hartwig, the president of the Insurance Information Institute. He says the federal law passed in 2002 requires providers to offer every business the option of buying terrorism insurance.

"It is important to recognize that each business that does not have the coverage made a conscious decision to not buy that coverage. They have to decline the coverage," Hartwig said.

He said insurance companies are worried about setting a precedent.

That means Tony Caz would be out a huge chunk of change, around $80,000. Caz is the co-owner of the Rattlesnake Bar and Grill on Boylston Street. After the bombs went off, no one stopped to pay their tabs. The Rattlesnake did not buy terrorism insurance, which would have cost about $9,000 per year.

On the pending federal designation, Caz said he’s preparing for bad news.

"I would think it is an act of terrorism. Hopefully the insurance companies, they might give us a break," he said. "I don’t know. We’ll have to see."

Insurance is sometimes called the cost of doing business. For many around the site of the Boston Marathon bombings, they may have to pay for not buying terrorism insurance with the cost of not doing business.