cyberpower is cheap, you can pick it up at microcenter. at least 1000VA, but I would check with douthitt . You might need more since it has a heater. 1400VA seems to be reasonably priced. Once you get into 2k and 3k units they get EPXPENSIVE!
APC, in my experience, has been more reliable with batteries that lasted longer. They are usually a lot more expensive and their quality supposedly went down some over the years. Still, for something expensive it might be worth spending a little bit more.
pierre