Off Season project

I know the season isn’t really over but some of our member got bored so we are talking about doing a paint ball robot. We were thinking about sensors for it and we are going to take the camera from the Vexplorer set but it on the CMU cam servo XY thing. Also we were thinking about a range finder, then doing a little projectile motion calculations (I already wrote the algorymth based on a input of meters and an output of degrees from horizontal) How much would a rangefinder that could do ~30m max and 10m minimum set us back? HOw do they work? Ultrasound? I kan haz hailp? kthnxbai.