I have been shooting landscapes for over a decade and honestly, the sticker shock for full-frame glass never really goes away. I remember my first trip out to the Columbia River Gorge with a cheap setup, and I was so worried my gear wasnt good enough. Trust me, you can get incredible shots without spending thousands. In my experience, the Canon RF 16mm f/2.8 STM is basically a steal for someone in your position. People on YouTube get all technical about barrel distortion and software corrections, but the RP handles all that in-camera automatically. I have used this lens on long treks where every ounce matters, and its so light you basically forget its in your bag. Here is why I think it fits your Portland trip:

• 16mm is perfect for those tight forest shots where you want to look up at the giant Douglas firs and get the whole canopy in frame.
• It is wide enough to capture a massive mountain peak and a wildflower field in one shot without having to back up into a bush.
• At f/2.8, you can actually do some decent star photos if you end up camping out. If 16mm feels way too extreme for you, look for a used Canon RF 24-105mm f/4-7.1 IS STM. It is usually the kit lens people sell for cheap when they upgrade. 24mm is the classic landscape focal length and much easier to compose with. I have tried many lenses over the years, and while the expensive ones are technically sharper, they wont make the hike any more fun than these budget gems will. Ngl, that 16mm is just way more fun to shoot with tho...