Priebus has already said that no way no how is Aiken getting a dollar of the party's money. So unless a couple of super-pacs can be rounded up then Aiken is on his own.
This wouldn't be the first time that Priebus had to backtrack on his words and it won't be the last. He'll just have to suck it up and write the check or assume the responsibility for a lost Senate seat for the want of a simple check that was under his control.