I am not sure whether it would suit your purpose, but I have been using a 800VA UPS by Cyber Power. I had got that more than a year ago, and it has been serving me well all the time. I got it for 1.6K at that time. So, if there is no reason that you want an OLD/USED UPS only, you could consider this one.
I am not looking for a sale of my UPS, though.