If people are interested I'll put something together.
Cost - let's keep it low, I have two spare rooms and a decent sized sofa, so kip at mine and you can experience the delights of the local 'ye olde cider bar' in the evening too.
I won't book a boat, rather if people are interested, then I'll book us on whatever else is going out those days - there's enough going on within driving distance to make that feasable.
Cost then, I'd guess at about £20 to £25 per dive plus fills and whatever you want to spend on beer and cider.
Travel - the local airport is 15 or so miles away and is served by FlyBe (who may or may not lose your bags), we have a mainline train station, and we're just off the end of the M5. If anyone is flying and wants to stay on the Sunday night as well, then no worries - I have to pass exeter airport on the way to work anyway, so I can drop you off.
Let me know and I'll get it sorted.
Numbers wise, I can probably accomodate about 6 maximum.