Well, the options (if the quite wonderful looking Orient Express mentioned above isn't going to work...) are:

• Flight with Air France or Alitalia. There are no discount one-way fares, so you'd have to do a throwaway. It's a fairly bog-standard flying experience - rather like a domestic flight, as they're both Schengen.
• Flight with easyJet. It's one of the better budget carriers, and does fly to Venice proper, rather than Treviso. It'll be a little less pleasant than AF/AZ, but not significantly for this kind of difference. Plus, the money saved will easily pay for a boat transfer on the Venice side
• Artesia train journey. It's quite a distance, so it's best done overnight (unless you want to get the Artesia TGV to Milan and change). There are 2-person sleeper compartments. If you enjoy train travel, there's nothing quite like arriving in Sta Lucia station early in the morning, walking out and seeing the Grand Canal right in front of you.
• Train journey in stages. Unlikely to be a good option when time is limited, but you could have a nice couple of days on a TGV/Cisalpino route stopping over in Switzerland, with some rather stunning scenery, too.