I am tryin to find more information about taking a sleeper train from Paris to Venice and how much that will cost? Also I want to find out where I can buy the tickets and if I should buy the tickets now or buy them when I get to Paris?
Night trains are popular and the most desirable accommodations sell out well in advance. If you wait until Paris, you probably won't find accommodations available. The cost varies by the kind of accommodation - reclining seat, 4/6 person cochette, or single or double sleeper, w/ or w/o toilet. You can buy the tickets from RailEurope, but that will be about the most expensive option. You might find them available from French Rail. If nothing else, you can book Paris to Venice via Munich on German Rail. The trip will take longer, buy you could buy it now. Leave Paris at 13:08 by ICE, as low as €39 with advance purchase. Get to Munich at 19:33. Take the CNL train from Munich at 21:02, arr Venice 6:38. I found one person in a deluxe (WC, shower) double for €149 for several dates.