You are welcome! The Italians are notoriously late in loading train schedules, keep checking back and they should be loaded in the next week or two. The route going through Milan is the quickest, most direct train route from Venice to Nice. A word of advice if you do decide to do this in one day rather than spend the night in Milan - Trenitalia shows there is a 45 min. connection time between trains in Milan, which should be fine. When I did this route last month (in reverse), my connection was only 30 min. and for some reason the train arrived in Milan 30 min. late (not sure why, as it left Nice on time). At any rate, I had to literally run across the station to catch my train to Venice. I made it, but just barely. The current connetion time of 45 min. should be plenty, but if you want to play it safe, you can take an earlier train from Venice to give yourself extra time. For instance, instead of leaving Venice at 11:50, you could leave at 10:50. This gives you an hour and 45 min. in Milan, which should be more than enough. You can always grab a snack and coffee in the station to kill time. There are trains hourly from Venice to Milan, it's the direct Milan-Venice Thello train which only runs twice a day.
I don't know of any other airlines flying that route that cheaply. Most others are not direct flights and involve a change somewhere else. Skyscanner.com is the best site I know of for showing most flight options, so check with them.