Ferries to Holland

Hi! I'm just starting to investigate the likely costs of various ferries to Holland. They vary a little from day to day, but generally P&O Ferries Hull to Rotterdam comes to slightly over £220 return round about the time we want to travel, while DFDS Newcastle to Amsterdam is only a little over £170 return. Another possibility is Stena Harwich to Hook of Holland, which costs anything from £68 to £132.