Cheapest & most efficient travel from airport (Marco polo) to San Marco district Venice
Bus to Piazzale Roma, then Vaporetto to San Marco
or
Alilaguna boat service directly from the airport
https://www.veneziaairport.it/en_gb/transport/transport-services/train
See Aussie’s post in this thread
https://community.ricksteves.com/travel-forum/italy/getting-to-venice-from-airport
Headed to Venice on a tour with RS in a couple weeks..... the RS Italy travel guide, starts page 120. Describes all possibilities of getting from airport to Venice. Thank you RS.