I am planning to build a single server machine which is highly dependent on data residing in RAM for performance reasons. I am looking for a UPS which can power the PC during a blackout (very rare) and when the battery level is like %20, it sends a signal to Windows 2008 to shutdown. Even if it's only for a few minutes, that's good enough. This is for home use so I am looking for an inexpensive unit ( less than $300? ).
Which brand/model is good choice? I prefer one whose battery is easily & cheaply replaced.