The cheapest supported camera, aside from a given you as a gift, is Jooan A2R from Temu. It is like $3 per piece, brand new. It is a nice little pan/tilt model with a low-end 720p sensor. But it is fast, nice looking, snappy and dirt cheap.
I'm seeing $9.66 on Temu. The description update on this video explains that it's due to tariffs (is it cheaper outside the US?):
https://www.youtube.com/watch?v=wfeA8wOEe34
The price fluctuates for sure. I bought 9 of these cams and my average price was right at $4... but now I'm seeing them closer to $10 and i can't recommend them over the Cinnado which you can often get for $10.