http://www.Delta.com Check out Orlando (MCO) through Atlanta to Manchester, England. (MAN is the 3 letter for that airport)

Once in country you might be able to ride on one of the local airlines (Ryan Air) to Dublin cheaper than renting a car and taking the ferry.

Oh, and they drive on the other side of the road so be very carefull if you are driving, or when stepping off a curb out of the Pub! Lots of Americans get hit crossing the road looking the wrong way for traffic.