First of all I have not looked at any of the links above, but here goes.
Two of the UPS units I use are from Belkin, although pretty expensive when they were new (I purchased them second-hand)
One of which is a 325VA and another is 625VA.
Both of which would give about 15+ minutes to shut down the system in the event of a power-cut.
Another I purchased recently 800VA for £46 manufactured by "Trust", also give about 15 - 20 minutes to shut down the system in the event of a power-cut, but that time depends on the load being drawn from the unit.
Both the 625VA and 800VA units comfortably run my system even when "everything" is switched on.
(2 PC's, 3 Monitors, 2/3 Printers, plus a few other bits and bobs)
The 325VA unit is only powerful enough to run a reasonably basic setup.
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1. Not all UPS systems come with automatic shut-down software. (The more you pay, the better the UPS)
2. The battery is the same type as used in most burglar alarm systems, for the 625VA unit cost a little over £10 a couple of months ago from my local CCTV and Alarm security people.
3. Some models have normal 13 amp type sockets whilst some have 10 amp (kettle type) sockets.
One little trick is to connect a "Multi-gang" trailing socket to the unit, then just plug all your equipment into that.
4. As far as I know, all UPS systems also have built-in ant-surge protection.
5. Running costs range between 20 and 40 Watts for the above units.
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EDIT
Changed Kva to read VA
Link to Trust.com
http://www.trust.com/search/default.aspx?search=UPS