I remember my first trip out west with just a standard kit lens and I felt so restricted... basically couldnt fit the scale of the landscape in the frame. I eventually picked up the Canon RF 16mm f/2.8 STM and I have been super satisfied with it. It is tiny but gives you that massive perspective you are craving for the Grand Canyon. A few reasons I love using it:

• It is way under your 800 dollar budget.
• 16mm is extremely wide, perfect for those huge vistas.
• It weighs almost nothing so hiking into the canyon isnt a struggle. If you want a bit more flexibility, the Canon RF 15-30mm f/4.5-6.3 IS STM is another solid pick that fits your price range perfectly. I used it for a while and honestly had no complaints, it works well for basically any big scenery shots.