If your willing to spend a little over $100...sometimes less even, you should be ok with a computer type UPS. There are some out there that are designed for very short amounts of time and others that will last longer. If your good with numbers (I am not) you could easily figure out what types of units and how many you would need.

UPS's are not based on a set amount of time. When your looking at specs and it says "20 minutes" or whatever, take into consideration that this is probably an estimate of how long the unit would last at full load. A desktop computer may be pushing 500-600 watts just within the tower, monitors vary (CRT's draw alot, LCD's do not). So if you have say a small rack with 20 feet of 3" flexwatt drawing 2 watts per foot (this may not be accurate but just a number) you would only be drawing 40ish watts of power which is no where near the UPS full load capacity. Because your at such a low load, the actual "up time" in the event of a power outage would be greatly extended beyond the "advertised" time period.