your right (they're marked up big time), i have a few monster PS that am using but i got a deal on them, the other reason for using them is cleaner power, its no joke. if you have hi end audio or tv and other units hooked up, having a decent PS help..
If you've already invested money into high end computer or home theater equipment you might as well spend that little bit extra and buy yourself a decent battery backup. I don't mean one of the cheappy ones I mean one that outputs a sinewave, has AVR boost/drop, surge protection... It always boggles my mind when people spend 10K on their home theater system and then get cheap and buy a $10.00 surge protector to protect it all. It pays to have it done right the first time.
Joe