Depends on the quality you want. Cheap solutions are about, but the quality is poor. A decent solution will cost you £200 each just for the cameras. Looked into it once for a customer, outdoor cams have different requirements for vision distance at night, usually a built in IR unit can only see 10' at best. As well as cameras you need either a PC or a recording unit (essentially a HD in a box). A PC is preferred, but it means leaving a box on 24/7 and of course it will get stolen, so has to be uploading to the net.
As lots of laptops now have cams in them, I'm tempted to write something to grab pics of the user and FTP them up to my own webspace along with IP address it is using. If it had GPS I could find the bugger too.