Depends on the company, the firm I use have a reasonable hourly rate and itemise pretty much everything, my alarm is more for the wife than anything else - when I'm away she wants to feel secure and activates the alarm when I'm away in nighttime mode.
The ones to watch for are the "package" ones where there is no breakdown of the costs of the components or installation and also if they offer direct monitoring and police alerting and have their own clearance. if they don't avoid.
They are less of a deterrent though unfortunately. I was broken into a few years ago in my previous house and the alarm went off and cops called, didn't stop the ****wits rummaging through nearly every drawer in the house, stealing a couple of items of the wife's jewellery and ****ing off. Cops aren't interested and by the time they arrived they could have made a steak dinner! Apparently jonny criminal carry cash for gold free post pouches and all they are interested in is gold to post off to the legal gold handlers! Cops never catch them with any of the stolen stuff on them.