Best UPS I've used so far for consumer use (I have two of them!): CyberPower CP850PFCLCD.
There are lower-capacity models of the same type which are less expensive that would still allow you to run that amount of wattage for probably 30-45 minutes.
The one advantage these have is that they're sine-wave PSUs, not "stepped" or "simulated" sine. There are a lot of benefits to this, especially with picky hardware. The user interfaces on them are wonderful too -- plus they let you monitor all sorts of things (in/out voltage, frequency, amps and wattage for power draw, battery time remaining, event count (for black-out or brown-out situations), etc.). They're great. Their customer support is fantastic too. My story: »Re: UPS on computer
This comes from someone who used to use TrippLite UPSes exclusively until recently. For datacenters I use (well, used) APC.--
Making life hard for others since 1977.
I speak for myself and not my employer/affiliates of my employer.