We are trying to plan the best transport between and York and Dublin. We are considering the ferry/train option but also interested in flying to save time.
Train and ferry is a bit of a slog. Over 9 hours, but it only costs £41, even travelling tomorrow. Use the journey planner at http://www.virgintrains.com/ and specify York and Dublin Port (Stena) as the start and destination. Flying. Ryanair have flights to Dublin from Leeds Bradford airport. See www.ryanair.com . See this page for your options on getting to the airport from York, a trip of just over 30 miles - http://www.leedsbradfordairport.co.uk/getting-to-the-airport
You also could take a longer train ride from York to Manchester and fly from there to Dublin. You'd have more departure times from which to choose and you could fly either Aer Lingus or Ryanair.