best thing to do is try NUTT travel..
This is run by Billy Nutt (race organiser) and father of racer Marty Nutt and they do great deals for bikers.
for example... return sailing bike and rider plus entry to the BSB at knockhill in July £89
can't get better than that
the ferry alone just booking direct was gonna cost me more!!
their phone number is 028 7035 1199 they get discounts from any port you wish