I'm going with the assumption all calendar days offer the same tour, 1 tour a day, happening at the exact same time. But some days are more expensive than others. Price is set per person/seat. You would like visitors to sign up for a seat.
Because you're showing a couple pieces of info for each day. It's likely going to be too cluttered/confusing to try and pack all of this into a single calendar. I would recommend a 2 page approach to help solve probably your main goal of getting visitors to sign up.
Something like this:
download bmml source – Wireframes created with Balsamiq Mockups
The basic info that influence the visitor's decision goes onto the calendar: Date Available, Price, # of Seats remaining. Then if the visitor is interested in a particular date, they click into the details page for the day. That'll allow them to read up on the particulars of that day's tour, including time, tour size/number of people already signed up etc. This will lead naturally to your call-to-action at the end there for them to move on with signing up/booking.