I use a low cost laptop ($500) plugged into a 24 inch monitor (second hand $100). Internet access is provided by a 4G wireless modem ($50 plus $15 a month for access), plugged into a router configured to limit bandwidth ($100).
Behind the monitor is a web-camera (under $100) with a clip on telephoto lens (under $20). The camera is on a telescopic tripod, so I can push it down out of sight behind the monitor, when not in use (and so it can't see me). I appear in front of a folding green screen (second hand $10, plus $5 for green paint). There is a sound absorbing pin-board behind the monitor, which can also b used as a green screen ($30).
Under the desk is an Uninterruptible Power Supply (UPS) , in case mains power is lost (UPS $10 secondhand, new battery $50).
Beside the monitor is a ring light for better illumination ($10) and my smartphone ($500). I dial-in to the video conference to provide a more reliable audio channel, and as a backup in case the power, laptop or primary Internet connection fails. Also I can monitor how well the audio and video is received using the phone.
I have an ergonomic chair to provide comfort (free second hand). The blood-pressure monitor is just to remind me how stressful online learning can be. ;-)
For a more advanced setup, see Nicolo Malagutti's "A bespoke audio-visual set-up" (2021).