No matter which route, it will take about 16 hours. As Tony says you can save on driving time if you get the Harwich and then Liverpool to Belfast (or Larne)ferries. I'm afraid that the Holyhead - Dublin ferry is one of the most expensive ferry crossings per mile in the world, especially towing a trailer. The ferry companies usually give discount for sporting events, but it is high season. I am sure that Barry, on the facebook site will have worked out a lot of answers already. Ask the questions. I am sure that he has already been in contact with the ferry companies.