I use a similar product like in the link below so the camera/lens doesn't have to be waterproof. Just cant find the exact one I have but check Amazon for other manufactures. However, people do use (that may be "cheaper") waterproof cameras with great results.
https://www.avastmarine.com/products/top-down-porthole-smartphone-edition
https://www.avastmarine.com/products/top-down-porthole-smartphone-edition