There's a motel about thirty minutes north of DUB on a rural motorway junction that calls itself the City North. That should do the trick, very handy for Belfast.

Reminds me (while we're off topic) of the cheapy transfer DUB < > Dublin city centre as friend told me about. Hop on the staff car park shuttle and get off round the back of Keeley's Lounge on the Swords Road. Dublin Buses stop opposite for a few €.