Group outings start at roughly €50-60 per person for a half day and €90-110 for a full day with lunch. Private boats are booked per boat, not per person: they already make sense from 4-6 participants.
Sailing is the most evocative and unhurried experience, ideal for couples; the dinghy reaches more coves in less time; the motorship is the family choice, with plenty of space, toilets and lower prices. Each listing shows the boat type, duration and maximum number of guests.
If the skipper cancels the outing due to unsafe weather conditions, you get a full refund or a free rescheduling to another date. The decision usually comes the evening before or the same morning.
In July and August yes: the best tours sell out, so it's worth securing your spot 3-7 days ahead. In June and September the day before is often enough.