Microcontroller interface and value

Hi All, I’ve been looking around to try and get a guage for how much i can charge to integrate a microcontroller with proximity sensor in a flash kiosk project. I recently started working with a microcontroller and an AS3 kiosk project came up, we are going to pitch the sensor to them… but i have no clue how much this kind of work is worth. I have it working, so if a person steps in front of the sensor within a certain distance it goes to the welcome screen, and if they go away it goes back to a screen saver. I looked around online but havent been able to find much information or anyone that’s doing this for clients.
-Ben