"We have nothing fear but fear itself" (Unless you sell video surveillance)
Being in 'the business" so to speak, the cost of maintaining CCTV systems is rather high.
Cameras fail for many reasons, not the least of which is environmental and since these cameras are outside, unavoidable. Pan/Tilt/Zoom (PTZ) cameras have many moving parts and they are prone to jamming due to spiders, frozen condensation, water incursion, heat, power quality issues etc etc. Figure about $4,000 per PTZ camera for replacement here in the US, probably much more in the UK. Even with "vandal resistant" housings, your "yoofs" will have tossed a few dozen beer bottle, bricks, rock etc at every camera in your area over the course of a few years and they don't make cameras resistant to "yoof" damage.
Our "yahoos" here would rather shoot at them so I guess you may have an advantage in the UK.
Under law of planned obsolescence, most cameras are obsolete in just a few years and the model number and price will have changed in 3 years.
If the system is an IP camera system, the network will inevitably go titsup at one time or another so that requires a lot of technical support to fix. Our rates are $ 140/hr but yours will be higher, I'm sure.
Have you ever priced a professional grade DVR or NVR? You think the server guys charge a lot? Just think about 15 to 20 TB raid arrays and a proprietary front end. NOT cheap.
This doesn't even cover the real costs, which are manpower. None of this video will do a thing for security UNLESS someone can actually LOOK AT IT IN REAL TIME! How many channels of TV can YOU watch at one time? Oh, you can't hire enough people? Then you need the system to have software that will look for specific events and send those to the monitoring station(s). More money, more F.U.D., Ad Infinitum.
Me, I hate big brother and want to get away from this stuff. Good Luck Folks, you'll need it.