The price is per boat or per group, not per person: private boat outings start at roughly €500-600 per day. From 5-6 participants up, the per-head cost gets close to that of a premium group tour.
Yes, that's the point of a private tour: you agree the route with the skipper or guide based on weather and preferences — more swim stops, a specific cove, sunset drinks.
Anniversaries, proposals, birthdays and holidays with small children, where flexible times and stops make the difference. Many operators arrange special set-ups on request.