Ringworm medication?

I just spent 110$ at the vet to get my 3 boys Revolution for their lice but the vet didn't give medication for the ringworm they possibly had. She wanted to do a culture but told me its another 83$ for the culture and I can't afford it right now. Is there a medication that I don't have to get prescribed by a vet that I can buy at the store for ringworm? someone told me I could use Canestin or Monistat does this work or what else can I use?

Thanks