there are a couple of sailings from dublin but these normally are booked full from the year before.your best bet would be belfast or larne at this stage,
the ferry costs 245 euro give or take a fiver,camping is 7 or 8 pound a night,i would recommend glen lough which is a couple of miles outside douglas and a lot of the irish lads go to it,good spot to camp and good craic as well.dont think there would be any need to bool but you could look it up online
have gone a good few and recommend it but the first thing you need to do is get onto the steam packet and see if sailings and dates suit you and take if from there