The most I ever spent was $40 CAD on a digital copy of wolfenstein 2 for switch -- I felt like such a sucker at the time although I got a lot of hours out of it in the end so I don't regret it.
I think the most I've ever spent on a digital title for PC was ~$30, but I only purchase DRM-free titles. Last physical PC title I bought was Skyrim (~$60-70) only to discover the install CD was basically just an installer for Steam. I was extremely annoyed and never bought another.
To answer your question, I think $40 CAD is my celiing for digital titles, but I usually refuse to spend more than about $20. That said, I could see myself dropping $50 on doom eternal when it sales if I can't get a physical around the same $