If you have your own transport, then Rochestown Park Hotel would probably be the most convenient - and the nearest. If you have no car, then you would be better off staying in a city centre hotel and getting the bus to Mahon Point. Jurys Inn would probably be one of the cheapest city centre hotels but, be warned - it is next-door to a hostel for the homeless and some people may have a problem with that. There was a thread about a year ago warning people not to stay there. Sorry, can't be more helpful.