Article: Official cults were state funded as a "matter of public interest" (res publica). Non-official but lawful cults were funded by private individuals for the benefit of their own communities. The difference between public and private cult is often unclear. Individuals or collegial associations could offer funds and cult to state deities. The public Vestals prepared ritual substances for use in public and private cults, and held the state-funded (thus public) opening ceremony for the Parentalia festival, which was otherwise a private rite to household ancestors. Some rites of the domus (household) were held in public places but were legally defined as privata in part or whole. All cults were ultimately subject to the approval and regulation of the censor and pontifices.

Now answer this question: Who funded non-official religious cults?
private individuals