UPS's dont cost over £200 if you go to the right place. The one that runs my server cost me £15 off ebay, and the ones that run my PC and Monitor cost me £20 from eBuyer.com (although they were on offer).
www.ebuyer.com is your best bet for getting a cheap UPS. Ive had many from them and they all work perfectly, even now over 8 months later. Just be aware that a CRT monitor may make your PC reset when you turn it on if its on the same UPS. Thats why I have 2, so it doesnt reset the PC, plus I get a longer backup time with 2.