There is a lot of info they need that frankly you can't trust the average client to accurately give over the phone. They need to know what your walls are made of, are they concrete, brick, wood or metal stud? Are they going to need masonry tools? What is the interior wall material; asbestos reinforced plaster is still not uncommon in older houses and if they're working with that the the price goes up dramatically? Is there electricity run to that location already or will they need a new circuit? If there is electricity run to that location does the existing circuit have capacity to handle the load? Is there even available space to mount the new unit? Is it in a neighborhood where it will need a cage around it to deter theives? And that's only some of the info they need.

About the only accurate price they could give you over the phone is the cost of the unit itself which you could also just find via a google search. The actual labor and other costs will vary by orders of magnitude depending on certain conditions.