why do you want an immobiliser? you should already have one installed... they come standard with AUI Futura - unless it has been removed?
This company, Brant is supposably well worth it
AA02 $ 398.00
TP3 " "
PGM3 " "
(all above are 3 point immobilisers not alarms)
I'm fairly sure you can get cheaper ones out there, theses are at the top end of the market