First, I do NOT recommend:
tour of the Grand Canal and San Marco bay; traffic, waves .. a nightmare; if you want to see the Grand Canal with only € 7.50 you can take the public boat n. 2 or n. 1 that leaves from San Marco Giardinetti and runs along the entire Grand Canal.
Costs up to 5 people for 30 minutes of tour: during the day € 80.00, night-time € 100.00
I always recommend asking the Gondolier for the small canals tour.
Explore the famous canals of Venice with a gondola ride, under bridges and along quiet stretches with an expert Gondolier.