I did some research in 2016 and ended up buying some "mydlink" stuff on Amazon.ca in 2016 and 2018. I wanted something affordable, quick, and easy for the front office and part of a warehouse at my moving and storage business. (See images of my purchases and a screen capture from one of the cameras.) Not high end, but I've been satisfied with the reasonable cost and ease of use. Wireless connection between cameras and recorder. Has sound and video. (The second camera has been more stable than the first. I have to reset the first camera every couple of weeks by unplugging it for a few seconds.)
I had an employee set up the cameras, recorder, and storage device, and connect to the internet. I then downloaded an app for my Android phone, and can view the two cameras in real time on my phone, from anywhere with an internet connection. Beyond the purchase of the initial hardware, there have been no ongoing subscription fees.
I also purchased some more extensive and expensive systems from a security consultant. They are a little better quality, but harder to set up and use.
For ease of set up and use, I would recommend the mydlink stuff.