The biggest cost factors
Camera count, building height, attic or basement access, finished ceilings, exterior conduit, recorder storage, and whether old wiring needs to be replaced can all change the price.
A clean finished-home install often takes more planning than a simple rough-in during renovation because the cable routes have to be hidden or contained properly.
Why site visits help
Photos and rough camera counts help, but they do not always show soffit access, wall cavities, power/network location, or ladder constraints. A site visit gives a much better picture of the real job.
It also lets the installer talk through tradeoffs: one stronger camera angle, a different recorder location, or a cleaner cable path may save frustration later.
Do not compare quotes by camera count only
Two four-camera quotes can include very different work. Ask whether the quote includes cable runs, terminations, weatherproof boxes, recorder setup, phone viewing, cleanup, and a walkthrough.