i have a couple friends that suppliy and fit alarms & stereos.
there is not the same mark up as you will get in a shop, one has owned skylines for years (32's and 33's). he is legit, not just some yarder
i got a paging alarm with knock & micrwave sensors installed, (and he got my mirrors to fold with the ignition) for under half the prices that i got quoted at strathfield and car toys.
PM me if u want details