quickymart: I seem to remember a UPS on sale in 2007 for around $130 that gave about 20 minutes of backup power. Would a similar type of device be sold today?
Check out the Constant Vigil link above. They appear to have a cheapie for $115, but I don't think it'd be gutsy enough to backup computers.
I've a couple of Dynamix UPSG750 SafeGuard 750VA that adequately power our computers, modem etc for around 15 minutes. When I get the new ONT I should be able to run it off those UPSs.