Canon's EOS Webcam Utility supports cameras down to the EOS 1100D, which, depending on your level of luck, you can find used under $100. Then all you need is a kit lens which can be found for very very cheap nowadays. Or, if you really think you won't be moving much, just get a super cheap vintage one.
Eh, I've had mixed results with Canon's EOS Webcam Utility and my Rebel T7.
I didn't see this documented anywhere, but apparently it's built only for Intel-based Macs. It'll still work on Apple Silicon, but only if the application using it is also built for Intel-based Macs. So you'd want to ensure you install the Intel-based version of Zoom, and then be careful to avoid it auto-updating to the version for Apple Silicon.
I bought a license for Cascable's Pro Webcam, and it mostly worked, but I'd often have issues getting it to initially connect to the camera and it'd sometimes cut out unexpectedly.
Give Camera Live[1] a shot. Canon's own software doesn't support my ancient Rebel TSi so I have to use this one instead, but it's worked really well for me. It connects using Syphon so matching up architecture shouldn't matter (and it works under Rosetta).
I use Syphon Virtual Webcam[2] to feed to Zoom, but you can also use OBS.
It's under 10fps for most of the cheap models. And unless you don't move at all the focal point of the kit lens is going to make the video almost useless. Autofocus on these cameras can't follow as fast as necessary for live video.
I have played with EOS webcam utility in the past and if you are not ready to spend big, DSLR is not the way to go.
I find it interesting that so many people talking about autofocus. My set up has everything on manual focus, and unless I use a 1.8f aperture, there's no need to change things unless I materially change the way I seat.
