Nearly $4 million of the total is covered by a Federal Transit Administration grant, while state and local funds are covering the rest, according to Keith Moody, interim general manager at CATbus.
CATbus announced in August that it had selected Proterra over two other manufacturers to supply the buses, but at the time it had not finished negotiating a contract.
CATbus has said it will use the 40-foot Catalyst E2 buses on routes serving Clemson University.
CATbus already operates six Proterra buses in Seneca, a deployment that Moody said has been a “total success” with more than 520,000 miles logged.
Proterra, which moved to Greenville as a startup in 2010, has sold hundreds of its zero-emission buses to transit agencies across the country.
Greenville is the California-based company’s East Coast base, home to its busiest factory, vehicle engineering department, and more than half of its 300 employees.