You can fit a swann camera for a lot less than the difference between the systems. I have one on the garage and covering the driveway to get Vehicle Registrations, as we live in a remote location with no neighbours. Pick them up from maplins for sensible money and can get some reasonable advice in store.
Did this myself and don't have a full on alarm system. The swann alerts me via email to my phone, took a half day to install 4 cameras, capacity for more if needed.
