My advice, since you are an experienced trailer-camper, is to stay OFF the #1 (Trans Canada Hwy) as much as possible. The roads may not be as smooth, but the prices are lower and people very welcoming.
Travelling from Ontario west, just past Wpg and Portage La Prairie there is turn-off to your right (north) called Highway 16, the Yellowhead. This will take you through many small towns all the way to BC's north coast. If you liker, I can pull out my Boler log-book and advice on nice/inexpensive campgrounds on that route.
Another alternative is too skim along south of the TransCanada, just north of the US border. Again, many small (and tiny!) towns with low low prices. Southeastern Sask has an amazing wonderful camping spot at "Pine Cree" where you leave the hot sun of the high flats and go down, down, down to a shady pine oasis.
I envy your trip!
That route sounds like a good idea. You are right, camping is expensive on #1as I did that trip in 2000, that time I had a 1984 Roadtrek, I would apreciate that info from your logbook