What you want does not exist. UPS units do go bad, and they not cheap to
fix. A properly maintained UPS unit needs the batterioes replaced at least
every 2 years. Additionally, the cheapest UPS that will handle 240V would
run you about $1000.

Also, the run times are very small. A "big" UPS for a computer can keep the
power for about 2 hours, and I am talking about a huge UPS for a PC.
Normally a UPS, used at it's rated power can give you about 30 minutes of
power when the batteries are new.

Anyway, the setup we use here is that we have all the PCs in the server room
attached to UPS units, but we have a generator that kicks in at an outage
after about 30 seconds of no power. Even with that setup some computers
turned off because of bad batteries.

I would just go for a generator if I were you.
--
gabriel