I have to say have been taking a few trips over by boat over the last few weeks and heres how I faired:
Prices for foot passengers connections
Irish Ferries & onward connection to manchester around €75
Stena line & bus eireann to manchester €72
Norfolk line €140 Dublin Liverpool (and that didn't even include Liverpool-Manchester!
Getting/buying tickets:
Irish Ferries & Rail - No bother, got from Connolly station!
Stena Line & BE - Could only get a single from busaras their allocation were sold out! got the return leg from the coach station.
Norfolk line- Website fares are cheaper, phone onsite purchasing sets you back with a €25 booking fee on top of things! My experience was the tickets were sold out but I found out only the cabins were! The cabins were default at 1 and read-only on the page and i had to go to the next day change this to 0 and go back to the day i wished to book. It then told me I had to select a cabin even though i said "0" cabins. There was no option of n/a and because of this I couldn't book the trip!
So I had to book at the port (phone bookings were closed!) Total price premium fare, (you had no other choice for the evening sailing but the evening and breakfast meal were included!) €140
On-board experience
Irish Ferries & rail- No problems on the train, virgin express had a shop on board and flew in change at chester arriva trains in wales hadn't but boy did it fly! i felt like we were taking off it was at the top speed alot. Irish ferries was grand had breakfast (at that hour of the morning! yes) slept in the bar area- alot of cowches and reclining seats as well upstairs- brilliant! bar and shop stayed open throughout the trip until the end!
Bus eireann/national express & stenaline- No problem here either. The bus trip took about 5 hours (because of stops etc) but had a great sleep on the coach (wasn't the same coach all the way, private operator to holyhead, then change to bus eireann) The ship was more or less the same as irish ferries but more or offer food wise etc. Pity you cant take the overnight stena ferry with the rail option. it doesnt take foot passengers.
Norfolk line- As a foot passenger, I hated it!
There were 3 foot passengers in total! On board the shop was a small area beside the front desk and there was no bureau de change was explained that norfolkline havent a licence to operate the cash. the resturaunt opened for the evening for an hour or two the meal was ok not great. Everything shut down by about 11:30-12:00. jsut slept on the couch. We were called for breakfast around 5 were late getting into birkenhead because of the space/allocation issues got in at around 6-6.30. In at birkenhead port £15 between the 3 of us £10 for a ticket Liverpool-manchester. even though I had the return ticket I chose not to return that way go by coach instead! I wont be going that way in future!
My recommendations would sail and rail or coach and sail with irish ferries or stena line with rail/bus connections