The $1 trillion infrastructure bill working through Congress stands to be a boon for school districts looking to buy clean-energy vehicles—and the bus companies that supply them.

The infrastructure bill, pushed by the Biden administration and passed in a bipartisan vote in the Senate, includes $5 billion to help public and private schools—and the private contractors who provide school transportation services—buy electric and low-emission buses.

Electric buses in particular have been a hard sell because they typically cost between $300,000 and $400,000, compared with about $150,000 for the more common diesel- and propane-powered vehicles, according to school district officials, state officials and manufacturers.

The nation’s fleet of roughly 480,000 school buses, some of which have been sidelined by the Covid-19 pandemic, includes about 1,000 electric buses, mostly ordered as pilot projects funded with a patchwork of grants.

Under the current legislation, half of the $5 billion is set aside specifically for electric buses—an amount that should enable the purchase of roughly 24,000 of them, according to White House estimates.

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The remaining $2.5 billion can be spent on electric or other low-emission buses that run on alternative fuels such as propane. Those buses are in the same price range as diesel models.

The two biggest school bus manufacturers in the U.S. are Blue Bird Corp. of Macon, Ga., and Thomas Built Buses Inc. of High Point, N.C. Supporters say a big cash infusion for electric buses will lead their prices to fall.

Blue Bird makes about 11,000 buses a year, half that run on diesel and half that run on alternative fuels such as propane, gasoline and compressed natural gas. The company has an electric line that has sold 775 buses over the past three years, said Trevor Rudderham, senior vice president of electrification.

Thomas Built Buses Chief Executive Officer Kevin Bangston said an increase in demand will also help supply-chain managers who order parts to make the buses, saying they are now “guessing at demand.”

The company, a unit of Daimler Trucks North America LLC, typically sells about 10,000 a year and has delivered about 50 electric buses.

Vice President Kamala Harris toured the Thomas Built Buses factory in High Point, N.C., in April as part of the Biden administration’s push for electric vehicles.

Photo: saul loeb/Agence France-Presse/Getty Images

Lower costs of batteries and increased demand have already led to price declines for buses made by Canada’s Lion Electric Co., spokesman Brian Alexander said, but he declined to be more specific, noting that school buses are typically bought through competitive bids.

Lion is building a 1,400-worker plant outside Chicago and employs a team of people to find grants for potential buyers.

Kevin Matthews, a lobbyist for National Strategies, a Washington, D.C.-based consulting firm, said the money would give a boost to a low-priority issue for educators who spend time worrying about class size, teacher salaries and student safety. Improving school buses, he said, remains politically popular.

“They are in every community in the U.S., and they aren’t blue or red. They’re yellow,” he said.

The bill directs the Environmental Protection Agency to award $1 billion a year in grants or rebates for the next five years for state or local governments, contractors, nonprofit school transportation associations or Indian tribes.

The money, the largest ever federal funding effort for electric school buses, could pay for the entire cost of new buses and charging infrastructure. The bill doesn’t specify how the program will distribute the money and what purchase limits a district could face.

Allen Schaeffer, executive director of the Diesel Technology Forum whose membership includes fuel suppliers and truck and heavy-machinery manufacturers, declined to comment on the bill, but said Congress shouldn’t favor one technology over another.

Sen. Jodi Ernst (R., Iowa) tried unsuccessfully to direct half of the funding exclusively for alternative-fuel-run buses. “Alternative fuels—like ethanol and biodiesel—offer consumers a cleaner, more affordable choice at the pump while supporting Iowa’s farmers and producers who feed and fuel the world,” she said.

Climate groups say electric buses could help the transportation sector cut down on the roughly one-third of U.S. greenhouse gas emissions it contributes. School buses travel fewer miles, making them smaller carbon contributors, but are seen as an easy sell to educators.

“I think every school district would love to go all-electric,” said Cathy Lin, director of facilities and operations for Arlington, Va., Public Schools’ 200-bus fleet. “It’s a healthier mode of transportation for our students.”

Under pressure from parents, Ms. Lin considered buying electric buses in recent years but couldn’t afford them. The district is preparing to buy its first three electric buses after securing a $795,000 grant.

An all-new electric school bus was parked beside a charging station at South El Monte High School in El Monte, Calif., last month.

Photo: frederic j. brown/Agence France-Presse/Getty Images

More than 600 electric school bus purchases have been bought with settlement money from Volkswagen AG over its emissions-test cheating scandal, according to World Resources Institute, a nonprofit given $100 million by Amazon. com Inc. founder Jeff Bezos to focus partly on electric buses.

Before his retirement in 2018, Kevin Downing recommended how Oregon spends its $72 million in Volkswagen money. It was still a tough choice to buy one electric bus over 10 less-polluting buses, he said.

“I don’t want to sound like I’m anti-electric, but from a limited funding perspective, I still felt compelled to spend it as broadly as we could,” he said.

Virginia’s Dominion Energy utility has proposed to replace 1,500 of the state’s school buses with electric buses by 2025. It plans to use the idled buses and their batteries, which hook up to the grid to charge when not in use, as electricity storage facilities.

Lawmakers remain under pressure to do more. Last week, the American Lung Association and other nonprofits told Congress that toxic diesel fumes harm developing lungs of children who breathe faster than adults, exacerbating asthma.

“This is a good investment—in public health, in education, in our economy and in our children’s futures,” they said.

California’s Twin Rivers school district near Sacramento, whose roughly 5,000 riders live mostly in low-income neighborhoods, bought its first eight electric buses in 2016. Ninety percent of its 130-bus fleet will be electric within the year, said transportation director Tim Shannon, adding that students prefer the quieter ride.

“They don’t have to yell and scream to talk,” he said.

Write to Katy Stech Ferek at katherine.stech@wsj.com