My rank order for investment:
1. Mic - See my mic comment in another thread
2. Lighting - It is hard for good cameras to compensate for poor lighting. Good lighting on the other hand, does compensate and helps laptop webcams perform much better. I currently run a Godox ULC60bi with a huge parabolic diffuser. Probably overkill for many. You can get cheap fluorescent or LED lights with a diffuser. Would avoid a ring light especially if you wear glasses.
3. Camera - I have used Canon M50 and Sony A6500 as webcams. These days, I use an Insta360 Link. It's not quite as good as the cameras (you can add more "background blur" with their software), but it's more convenient. I still get compliments on this.
4. Background - Blur, doors, and bedrooms are what you see 90% of the time. A good background helps you stand out. I have a bookcase with the books ordered in color. Folks always comment about it. There are lots of other common looks, look on Youtube or X (Kevin Shen) for office makeovers.
5. Teleprompter - Not for scripts but for "looking in the eyes" of my students or the person on the other end of the call.