I'm not really an expert on it, but generating pulses and detecting time for laser bounce is quite hard I think, which is why the laser distance measurers cost so much.
You'd need to be able to resolve a time period of the order of nanoseconds or less I think, for a decent resolution.
There is an alternative method, which uses the idea of shining a laser spot, and observing it with a camera which is offset from the laser by a known separation. By looking at where
the laser point is as viewed by the camera (it will be the brightest spot on the image), and using trigonometry, you can work out the distance. It is quite popular with the
robot experimenters community.
If you wanted to do it the first way, then the cheapest method would be to use an existing laser distance meter, and hack it. Or you could try to purchase a module but it may be
hard to find. I think Leica make most of the modules in commercial laser distance meters (even third party ones possibly).
If you just want an approximation if something is present 2-3 meters away or not, then some other technology may be cheaper, e.g. ultrasound maybe, or PIR if they are moving.
Depends on your application. Lots of experimentation will be needed regardless of the method chosen I guess.