As I see with camera systems the expense is not the camera itself, but a decent infrastructure to it. DVD recorder/HDD, that thingy which sums up the several camers's picture into 1 big picture plus you need a tasteful solution for the cables or for cable less versions keep exchanging the batteries.
You could probably get a free one thats obsolete and being thrown out, not necessarily broken either, just replaced.
Good idea Rai, do you have an idea where should I start looking?
My father's business had a few things stolen from the lobby and we were thinking about getting cameras (expensive) or fake ones.
But the best would be of course to get an obsolete one from somewhere.
I really find the idea of alarm subforum interesting. This is a particularly foggy area, or at least I know woefully few things about alarms, but I hope I'll find remedy to that in this subforum.

PS.: What exactly does it mean that the forum is restricted? Apart from "do not redistribute"?
Is it closed to unregistered users?
As my first contribution to here I found an interesting but older book called
Alarm, Sensor & Security Circuit Cookbook (1994) By Thomas Petruzzellis.
It is probably outdated(how much I don't know, maybe someone else tells me here?),
also possibly not the best book in the universe but since it's the only one I read about alarms, this is the best one I read on alarms. Ever.

EDIT. The moment I step out tothe Alarm subforum I realise that his book is already recommended thare by 10ringo10...

Small yappy dogs are the best deterrent.
They feed them a bit of dog delicacy soaked in some sort of strong sedative or sleeping pill...
To infinity... and beyond!
=== WARNING DANGER OF TYPOS!===
Arfspeak: calnin cladycomes: you allow her key in themodning
Equals in plain English: cleaning lady comes: you allow her key in the morning