I use seafrance a lot, they usually not expensive and as a big bonus will normally allow you to take any -ealier- sailing at no extra charge.
For the cheapest sailing HU have now persuaded Speed ferries to charge half price for all bikes ( they were same price as cars up till this spring ). this means bike and rider can travel for as little as £9 each way. ( depends on time of day )
also note they go dover to Boulogne not calais.
see what you can do at the dates/time you want.
http://www.speedferries.com/
I just checked, sorry best I can do is £38 return on those dates
[ This message was edited by: panda on 2006-07-12 15:08 ]