There is an train once a hour from Venice via Bologna (ESAV to Bologna, 16 minute transfer time, then regional train to Ravenna). Price 33.80E.
There is one evening train that goes via Ferrara, both legs are regional trains, the total journey time is the same 3 hours, but the transfer time is 8 minutes. Price 10.40E.
Is there any reason to think that I would miss the connection in Ferrara? With a price difference of 23 euros, I'd rather spend a little more time in Venice and arrive in Ravenna at 9.45 pm.