So... there are two types of tariffs for trains in Europe, one is domestic (each country/railway company sets their own tariff) and international (this one is used for standard international travel and for purchasing tickets not in the country where you plan to use it, like buying Budapest-Vienna ticket in Berlin etc.). TCV tariff or as its now also called - SCIC-NRT is one of the international tariffs.
Generally domestic tariffs is almost always cheaper, than international, but in some cases it is not like this. So it makes sense to purchase international ticket for domestic/within country use instead. But such "trick" is only useful only if you intend to make multiple stops on your way (in your case in Visp, Brig, Domodossola etc.). Is it your intention?
If you need only to travel from Lauterbrunnen to Vernazza in a cheapest way, then it's better to follow other option: SBB (Swiss railways) sells special discounted tickets for travels from Switzerland to Italy, but those aren't sold from any station. Closest to Lauterbrunnen station from where you can buy such discounted ticket is Spiez (only 20 minutes from Interlaken). As of now Spiez-Milan discounted tickets for October 23 are sold for as low as 30 CHF (32 CAD). Can buy those here -
https://www.sbb.ch/mct/wi/shop/b2c/pipSchritt_0.do Lauterbrunnen-Spiez one way standard fare is 17.2 CHF (18 CAD). So full route Lauterbrunnen-Milan will cost you only 47.2 CHF or 50 CAD.
Standard fare Lauterbrunnen-Milan is 98 CHF, that is the price you'll pay if you purchase your ticket at the Lauterbrunnen train station. As you can see, it really makes sense to purchase discounted ticket from Spiez online in advance + standard till Spiez, in such way you'll save app.50%
For Milan-Vernazza part it's much better to purchase domestic Italian ticket instead of international one, since Italian domestic tariff is rather cheap. Standard fare starts from 12.7 euro (18 CAD), most expensive option involving faster InterCity train cost 22.3 EUR (31 CAD)
Resume: you can make whole Lauterbrunnen-Vernazza trip for as low 68 CAD, which is quite good price for such route.
p.s. feel free to ask additional questions in case you having troubles with any of the above info