I have checked prices for rail travel using a select pass (2 people traveling) three countries:
 
Itinerary:
 
Geneva-Rome (overnight, double sleeper)
Rome-Venice
Venice-Paris (overnight, double sleeper)
 
Price (Canadian) inlcuding the 2 railpasses, and the reservations, is $1432 (or around $1234 USD).   I know that we can reserve in Europe…but do not want to risk not having space on the night trains.  Price at www.raileurope.ca
 
If traveling on overnight trains, we would want a double private sleeper.  
 
The other option we are considering is to fly with the discount airlines (this would add several nights hotel costs, plus transfers to/from airports, although the strict transport costs would be a bit cheaper).
 
We have never been to Europe before and any advice would be appreciated on whether you think that this price is reasonable, or if it would be better to pay the extra nights hotel/airport transfers and fly between these cities.    We need the help of people who have done this and so know what is feasible or not both in terms of the price and time each option would take.