Small-business owners generally face higher per-person insurance costs for themselves and their employees than large employers, because individuals and smaller groups are inherently more risky to insure — and, therefore, more expensive — than the larger pools that big employers can assemble. The Affordable Care Act tried to address some of those problems by requiring insurers to set level premiums for all individual policyholders by age and by prohibiting insurers from dropping policyholders if they got sick.

One in five people who buy coverage through the marketplaces created by the law is a small-business owner, totaling 1.4 million people, according to Treasury Department research. Another significant population relies on government programs like Medicaid, which the health law expanded.

Joel Schaubert, 51, a software consultant in Minneapolis, said that before the law, he worried about what would happen if he harmed his left arm, which he broke a decade ago in a biking accident. It became a pre-existing condition, and as he navigated the individual insurance market, the policies he bought explicitly excluded it from coverage, he said. That changed only after the health law took effect.

“I can finally get insurance that covers my entire body,” Mr. Schaubert said.

But to expand coverage and bring in enough healthy customers to keep various insurance pools afloat, the government also forced some trade-offs. To put more people into the individual insurance market, it stopped allowing sole proprietors to join small-group pools and required them to instead buy individual coverage.

The intention was to prevent groups from cherry-picking healthy participants, but it had the side effect of significantly increasing costs for some sole proprietors. The rule also forced a number of professional associations to cancel the plans they offered members.

Leah Gomberg, 48, a home stager, and her husband, David, 50, a self-employed psychologist in Maplewood, N.J., used to purchase coverage for themselves and their three sons through a broker who bundled their business together with others into a small-group pool. Now, they pay about $1,800 a month, twice their previous premium, for an individual family policy with a narrower network and more out-of-pocket costs than her previous one.

“It’s just sucking the life out of us financially,” Ms. Gomberg said.

For some entrepreneurs, the individual market’s combination of pricey premiums and high deductibles puts any plan at all out of reach.