If you look around or know someone who works in an office building with access to "old" equipment you can get some pretty expensive UPS units for dirt cheap. I know of one company that purchases all of their UPS units new and then when battery replacement is due in three or four years they yank the whole unit and replace it with a new one. They're practically new but they dump them for about 1/4 of the original price. Toss in $60 worth of batteries and you're good to go.
That's what I do at work and home, with our Triplite UPSes for workstations. 180.00 for a new one vs 75 for the batteries.