you can adjust the sensitivity - where you install the sensor makes a huge difference, so mount it and then adjust accordingly.
I paid $150 (delivered/ebay) and installed it myself, it was my second alarm installation and really took my time with it so its much neater/tamper proof than my last effort.
I think the difference between the 60 and 80 series is the number of immobilisation points, mine is only 2 point but is still black wired standards approved etc.