Hello,
As I see it you will need the Arduino to read the sensor and the laptop to take a picture with it's camera, once the sensor was activated.
This is generally easy and is done with Arduino and Processing, this together make two programs one on the Arduino that reads the sensor and sends the data to the other running on the laptop. Then the laptop software takes the picture.
It might look a bit complex but I think it's a one day work at tops, more can be spend on some small changes and calibration, which of course is also a part of the price.
In general this is the price for the two programs and changes till you have it as you need it.
Hope to hear from you soon,
Mihail