Honestly, I would have no problem paying $299/yr for 10 cameras or even more if Sentry really dialed in their product which I am sure they are doing right now.
I get a little frustrated when Sentry is not working as expected or flags dogs as humans or fails to miss obvious human movement or flags a shaded tree as a human in the wind but I also try to keep in mind that while it's public, it's brand new and further tweaks are required.
I'm holding hope that their algorithm gets quickly!
In the meantime Im working on the standard included
BlueIris trigger settings to help eliminate false positives. I have 16 cameras on a property with 55 palm trees surrounding it and frequent windy days that throw shade around like crazy... plus a big dog that runs like crazy in front of half the cameras.