Yep, do a search, you'll find many threads.
I can confirm the APC BR1000G works.
I can confirm this APC Model as well but if you are only conserned about cost, Cyber Power are not bad so I hear, I've just been using APC for a very long time and they have proven reliability to me so I'll stick with them. I am evaluating a Cyber Power 1500VA unit, it was definately cheaper than the APC unit but I have no idea how long it will last. My previous APC unit lasted over 12 years, I think it was closer to 15 years and then I bought this Cyber Power unit.
Something you didn't state is how long you want the unit to remain on should there be an extended power outage nor how much power your unit consumes which actively in use, or if you want to power other devices with this UPS. I power my ESXi machine, network switch, router, and modem. Also do you have a lot of brownouts or short power outages? This all makes a difference when you need to select an UPS.
Also realize that you will need to configure the UPS to FreeNAS and you should test it as well.
As
@danb35 stated above, there are a lot of threads on this topic, do a Google Search on "freenas select ups" or something similar and I'm sure you will find something.