Yes, the Canadian is by far the most expensive. It is also the longest ride and the best views and best equipment. Don't know which corridor trains run Budd versus LRC. In March I took train 64 and it had LRC Business Class cars and Budd coaches. Be warned that the interior of the Budd coaches have been entirely renovated. The corridor trains do not have the feel of a classic streamliner even with the Budd equipment and the scenery is nothing to write home about on the corridor.
People take the Canadian pretty heavily both directions in the high season, it is also equally thin both directions in the winter, but again, I recommend eastbound. The heaviest load is always between Vancouver and Jasper. You leave at 8:30 pm, not 10 pm and you are pretty much guaranteed to see the Rockies. I would look at a shorter trip, like Vancouver-Edmonton with a lower berth if money is a concern. A discount lower Vancouver-Edmonton is $622.65 CAD in the off season including GST. Also right now the Canadian dollar is worth about $ 0.76, so that would work out to about $473 USD. The other trains are not near the experience The Canadian is. I say Edmonton because Jasper is a bit hard to access, unless you are doing a Vancouver-Jasper-Vancouver trip. Plus, you get dinner onboard, you wouldn't get any dinner onboard if you got off at Jasper, they don't serve dinner leaving Vancouver.
The Canadian really feels like a classic streamliner in the Super Chief tradition, especially in the off season when it isn't gargantuan. I can say that with some authority, having actually ridden the Santa Fe Super Chief (Via 1/2 still isn't as good as AT&SF 17/18, that train was in a very rarified class, but it isn't far off, either). It is the only train left on the continent that does. Next in line, but pretty big step down, is Amtrak's Coast Starlight when the PPC is running.
As to the accomodation charges you would get with a rail pass, that is easy. Zero. Canrailpass is not valid with anything but economy. Besides, that is not how Via prices sleepers anyway. They just have a fare for the sleeper, not rail fare + accomodation charge.
Oops, sorry, just saw the Canrailpass System Extra. That appears if you buy the Extra version of the pass, you get a 25% discount on the lowest available fare for Sleeper Plus. So you buy the pass and then pay for a Sleeper Plus ticket at 75% (Via does not price rail + accomodation like Amtrak does, they just have a different all-in sleeper fare). So let's say you get the "Extra" and go Vancouver-Toronto. You'd buy the "Extra" pass for 7 one way segments at $799, then apply one of the segments to a 25% discount on a Sleeper Plus lower berth Vancouver-Toronto off-season, which would bring the fare down from $1205.40 CAD to $904.05 CAD. If you do that, I hope you use the heck out of the other 6 segments, because you just spent $1703.05 CAD. Now, if you wanted to go on the Ocean or Hudson Bay, too, in a sleeper, the same thing applies. That adds up in a big hurry.
I don't know about you, but that math wouldn't work for me. If it were me, I'd fly to Vancouver and take the best part of the Canadian to Edmonton for a whole lot less money.