The superintendent of the statewide charter school district says at least $12 million is needed just to keep up with the system's growing student population.
Wayne Brazell says 10 new schools are expected to open this fall, including Bridges Preparatory School in Beaufort. He expects at least 3,000 additional students and possibly as many as 4,000.
Currently, 11,600 students attend the district's 18 charter schools.
Gov. Nikki Haley has recommended an additional $5 million for charter schools in her executive budget. But Brazell says without at least twice that amount, charter schools could be in serious financial trouble.
Officials at Bridges and Royal Live Oaks Academy of the Arts & Sciences in Hardeeville said they were unsure what impact lesser state funding would have on their schools.
Charter schools are public schools that must meet all state and federal standards but receive flexibility and are governed by a board of parents, educators and community leaders.
Charter schools that organize under their local elected school board receive money raised through local property taxes. Schools organized under the statewide district do not.
Riverview Charter School, also in Beaufort County, is chartered through the Beaufort County School District, so it gets its money from local property taxes.
Riverview, then -- like other public schools in the Beaufort and Jasper county school districts -- gets about $8,000 to $10,000 per student in federal, state and local dollars, said Royal Live Oaks executive director Karen Wicks.
However, schools in the statewide charter district's get about half that amount or less. "Brick-and-mortar" schools, such as Bridges and Royal Live Oaks, receive $5,262 per student. The statewide district also includes online schools; they receive $3,712 per student from the state.
The difference in funding means a statewide chartered school must raise more money on its own to support instruction, including longer school days to help struggling students, Wicks said.
Royal Live Oaks' school days are from 7:05 a.m. to 4:30 p.m., with optional half-days on Saturdays.
The school has additional financial pressures because about 83 percent of its students are on free- and reduced-priced lunches, meaning they come from lower-income families.
Insufficient funding from the state could mean statewide charter schools would have to defer updating technology and buying newer classroom materials, and may struggle to pay teachers and maintenance costs for the longer schools days, Wicks said.
Financial challenges aren't the only difficulties the statewide charter schools face. Some have been criticized for poor performance and one is losing its charter amid allegations of fraudulent diplomas and financial discrepancies.
Staff writer Tom Barton, The Associated Press and The (Charleston) Post and Courier contributed to this report.