Where are you heading to in Norn Irn?
Ferries can be expensive, liverpool boat especially so. Belfast or Larne / Cairnryan may be cheaper.
Belfast international airport is outside the city (its nearer Antrim) Belfast city is much more central. Bus link to International is good, Taxi’s from the city are far more expensive than other taxis in the city. There is also the City of Derry aiprort for the north west. Car hire available from both, though if going to Belfast, you may not need one if flying to the City as the town is quite compact (depending where you are staying).
Drop me a line if you want an inside track on anything.