For distance, you either need very expensive synchronization between A and C (to try to do phase or time-of-flight) or, more likely, triangulation.
The "easiest" way to build for a hobbyist this would be to use two cameras that are rigidly linked, looking in the same direction. Also, a CPU of some brawn (say, 700 MHz ARM or better -- Raspberry Pi, BeagleBone Black, etc.) Run image recognition to find the lasered dot. Measure the separation (in pixels) in the two images to calculate the distance.