Agreed yamanx as a ballpark figure. The fares are regulated and published in advance. The bit they don't tell you is what discounting they apply to each sailing. This is a similar business model to other travel operators. There's a maximum standard fare and when things are looking slack, they offer limited discounts to try and entice people.

The 2015 maxima are here http://www.steam-packet.com/assets/pdfs/...cea14c2bbe

The most expensive prices are in the pink column and as you can see, a car plus 2 comes in at £233 each way. 2016 fares are yet to be published however the government regulate the increases and with inflation being so low and the falling oil price, I wouldn't envisage a big hike.