How much is it to go to Venice from Rome - I found flights on ryan air for about 45 euros

Have you added on the costs to/from the airports Ryanair use?

is there a difference in the airports - I know that the flights leave from campiano and go to Treviso

Standard fare on the EuroStar Italia is E44.93 for 2nd class and E67.14 for 1st class. However, if you book online well in advance at trenitalia.com, you can get either 1st or 2nd class tickets for E29. When they're gone, the price goes up to E39. When they're gone, you pay full price.

You don't go to either airport in order to catch a train therefore you don't pay to go to the airport. Factor in those costs - plus the time spent getting to an airport, checking in, passing through security, etc - before comparing "€45" against the train fare

Hello anitaseth. The Treviso airport is not the Venice Marco Polo Airport. The Treviso is a smaller airport north of Venice. There is a bus that will take you into Venice to the Piazzale Roma where you would than either walk, take the vaporotto or a private water taxi to your hotel. The bus from Treviso would probably take a good hour. Not sure of the cost. My opinion, I would take the train from Rome to Venice (to the Santa Lucia Train Station which is along the Grand Canal in Venice).

Train is a much better choice. No contest