Trouble with renting a car

We are traveling to Ireland in the coming summer. We have booked the plane to Dublin and an airbnb near Skibbereen. The plan was to rent a car in Dublin and drive half the way, sleep one night in another bnb, then drive to Skibbereen. The problem is that all the rentals that we have seen require a creditcard, which we cannot get. The plane is not refundable. How can we still make the trip? We have looked at public transport but we prefer to avoid that if possible. Is there any way to get a car in Dublin without a creditcard? Any help is much appreciated.