My officials discussed issues arising from your question with Insurance Ireland, who stated at the outset that ultimately matters related to payment method options are contractual ones which rest between the individual insurance provider and policyholder.
Insurance Ireland also pointed out that the majority of personal consumer insurance products can be paid in instalments and that it was not aware of any major difference in this respect with regard to commercial insurance products.
In respect of the average cost to the consumer for such a facility, this is not data which is collected by the Department or industry. While insurers are permitted to apply administrative fees in such circumstances, the amount or proportion charged varies between different providers.