The Palmetto State native wrote in an op-ed Thursday in The State newspaper in Columbia that his super PAC will bridge the gap after state Republicans refused to contribute anything above candidates' filing fees.
Earlier this month, Colbert offered Republicans $400,000 if they'd name the contest after him. The party said no, and Colbert says he started working with state Democrats to get an advisory referendum on the ballot.
The primary is expected to cost $1.5 million.
An Election Commission spokesman says the agency would need to ask the state's attorney general if it can even legally accept the money.
Colbert did not immediately respond to a request for comment.