The materials the installer is using make a difference. For example, PVC is more expensive than poly piping, but it lasts longer.
Other factors include whether it’s a new home or an existing home. It’s easier to install a system on a property that doesn’t have established turf.
Depth of the install is also important due to the freezing of the soil in the winter and turf maintenance requirements, like core aeration. You want it deep enough that it wouldn’t be damaged by aerating the lawn, which is important to turf health.
For more about lawn irrigation systems, read our article: Questions to Ask Your Irrigation Contractor.