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.
Hey, Openmiko is a nice project. With your baggage of knowledge, I would love to see you contributing to Thingino as well. While we still depend on binary blobs from the manufacturer SDK, there is a work on alternatives to replace what is replaceable with open stack. Join the team, have fun.