Hi all, DFDS (Newcastle>IJmuiden) quote 381GBP rtn this summer for 1 bike and 2 people in a cabin with shower. 20% more than this if not booked 30 days in advance. Reclining seats are all gone on many crossings.
For Harwich>Hook of Holland, Stena quote 184GBP rtn for 1 bike and 2 people in reclining seats (I couldn't find cabin prices online). Add the extra petrol needed to get from Newcastle or Harwich to Scotland and back, and total costs are pretty similar to Superfast's fares. No coincidence, in my humble opinion...
Having sailed with DFDS and Superfast, we'd recommend Superfast; ships are newer, cabins quieter, you arrive directly in Scotland and a bouzouki band plays a selection of Greek favourites in the bar :-)
Tip: take your own strap-downs with you to secure the bike on deck, and don't rely on assistance from deck staff. You won't get any, if our experience is typical.
TChallen, thanks for the tips and the excellent site...