I have 2 1500 va units on the PC's in the house here, they'll run a pretty strong system with lots of goodies for half an hour and huge amounts of time if everything happens to be off and just in standby mode.
My A/V system has a 750va unit that will run all the dvd player/recorders and TV for about half an hour if the TV's on and much more time if maybe one unit is recording by itself and everything else is standing by.
Bigger is better and true sinewave output with boost and buck is best but most cheaper units use approximated sinewave output and don't always do the boost and buck part which means they will raise or lower incoming voltage as needed in case of brownouts or surges(within reason).
None of my currently in service units are true sinewave but most modern equipment will be OK with it, some will not so double check before you plunk down your money.
Watch the office stores and sales on the bigger and smaller units happen all the time. My last APC one was 100 and it's a medium quality unit with a nice LCD display that shows all the important info you'd ever need.
My older one was like 80 out the door with a 50 rebate when they were closing them out so my final price was like 30 bucks, less then new batteries for all my older ones that finally ate theirs.
Watch the black Friday sales as I bet at least one office store will have a good deal on one or more, that's where I found my last one later in the morning because everyone was buying up all the really cheap stuff first thing and nobody wanted to spend 100 on a UPS
Also got a great price on a 2 gig USB drive that I will cycle into my media player system soon.