You could consider fitting just the Clifford Blackjax component at around £160 fitted. It's an anti-carjack device (or self-recovery device) that I've had fitted on all three of my CTRs.
It works as an immobiliser, however, it's used in conjunction with the revs of the car, pedal movement, door / boot / bonnet opening and a timer. When you get in, you tap the code onto a two-key keypad (combination of presses). If a door is subsequently opened and the code is not keyed, once the car is in motion, after 20 seconds you get four warning blips (to remind you to enter the code). If the correct code is not keyed within another 20 seconds, the ignition is cut in pulses (whilst sounding the alarm and flashing your brake lights to warn traffic behind) until the car is brought to a gradual halt when the immobiliser cuts the ignition completely.
The theory is that if you're car-jacked (or it's stolen), the thieves get a safe distance away before the car cuts out. When they leg-it, you return to the car, key in the code and off you go.
You can put it into a valet mode using your code, for servicing etc.
The only nuisance is if you or a passenger opens a door whilst the car's running, but you do get the warning blips and you soon get used to it.