Depends what your budget is, whether you think Ireland is worth the effort. Also what you personally consider "cheap". Everyone's views on "cheap" will differ. Price is also dependent on the size of your camper. Ours is a smaller size motorhome at 5.5 metres. We're also here for 5 weeks. For us, I think the ferry price is worth every penny. Also, you can't really get here easily in your motorhome any other way - maybe freight from Liverpool? I think that used to be an option, no idea if it still is...

We booked our ferry tickets several months ago, cost around the £400 mark (return) from Cairnryan to Larne, that included a little extra for flexi-tickets in case we wanted to change the sailing dates at any time.
Bodgerndog in Dumfries told us the other day that friends who regularly visit her every year are gobsmacked at the increase in price for their Amsterdam to Newcastle sailing! They always bring their dog with them. The price this year for that particular return ferry route ( 2 adults and a dog) is now just under the £2,000 mark... !!!

They are now looking at air flights that take dogs instead...