[PeterisP]

Free/cheap digital payments exist (eg. EU SEPA credit transfers); for credit cars, however, the majority part of the cost (and thus price) is not just making the payment but ensuring that payments are reversible in case of fraud and other disputes, and that customers can get their money back even if the money can't be recovered from a fraudster.

If you'd add a reputable escrow service, dispute resolution system and fraud insurance on top of any cryptocurrency, these features will drive the cost up just as high or more.