Lots of options, some cheap, some free.
Huge!!! rest stop on Hwy #1 just over the bridge as you leave Revelstoke. Washrooms included. A McDonald's and A&W are prior to the bridge. No overnight parking in front of these fast food joints though. No matter. Get your food and go over the bridge.
Further on, "Lakeside camping," says a handwritten sign at $15 a night in what looks like a loggers camp just after/before 3 Valley Gap.
About 25 kms west is a very nice big rest stop on the right hand side. Washrooms included. Great mountain stop.
Nearer to Sicamous is a Husky station with tons of parking space.
Take a turn away from Sicamous towards Kelowna. There is a very picturesque large rest stop on the right side, before you reach Mara.
If you are interested in a full hook-up, try Whispering Pines s little farther up the road. $40ish a night will get you a nice shady spot beside a burbling creek. Showers are good, not necessarily hot.
Sani-dump is free for registered campers; $5 for others.
There are a number of smaller, crescent turnouts not suitable for very large rigs, but smaller RVees or cars would fit perfectly. All include mountain views, a lake, or both. FREE.