OP is arriving at the train station-which one?
We would need to know where your hotel is to give accurate advice
The film festival does complicate things but $195 for a water taxi seems extremely high
Get Your Guide is a reseller not a tour company
Book a water taxi on the official site
https://www.motoscafivenezia.com/en/
I suspect a vaporetto will work for you but can’t say for sure without knowing where your hotel is
( really no such thing as a “public water taxi”)
There are threads here describing the various modes of transportation in Venice-you need to inform yourself of these options
A forum search should bring those up-filter by Type and Date
ETA
Except from Aussie's post- transportation in Venice
Water transport in Venice.
Gondolas. Only for pleasure, not for transport. 90 euro for half an hour for the boat, more for evenings.
Traghetto – big gondolas, two oarsmen, about ten passengers, for crossing the Grand Canal. Found at Rialto, San Toma and a couple of other places. Cost 2 euro per trip, can save a heap of walking.
Water taxis, which are like a floating limo, costs to match.
Vaporettos - ACTV. Are like a floating bus, operate on a bunch of routes. Get the app Chebateo for routes and schedules. Vaps do not service the airport. Vaps are not water taxis.
Alilaguna ferries, service the airport, run from Marco Polo via a bunch of stops to the main part of Venice, Murano and Lido. They stop at some, but by no means all, vaporetto stops.