This sounds like an American viewpoint. In Australia, New Zealand and much of Europe they are pretty cheap to install, and rarely require additional insulation.
It may be that they're relatively new to your area, so the demand is outstripping supply of installers who have been doing this for 30+ years and as such are charging to that effect.
It may be that they're relatively new to your area, so the demand is outstripping supply of installers who have been doing this for 30+ years and as such are charging to that effect.