If you want to play with this stuff today, comparatively simpler 2D scanning LIDAR can be found cheaply on Ebay.

You can usually find used SICK units there for well under $500.00 USD (I once scored one unit for $250.00); even when they look in terrible condition they usually function fine (they are designed for industrial environments and usage). These old units have a downside in that they use older serial comms (RS-232 and RS-422) that can be tricky to get going; for one unit I had, I had to send it back to SICK to get it reset to RS-232; it was originally set to RS-422 (faster), but to go back to the slower standard required a converter, which I didn't want to spend the money on if the unit didn't work properly. Then - on top of all that - I had to set up a Window NT 4.0 workstation to use the software. Plus they require a 24 volt DC power supply (great for mobility chair robots, though!). Once I got it running, though - everything worked well.

They are also large - as in coffee pot sized (in fact, they are kinda "affectionately" termed this), and made of aluminum casting and other metals that make them relatively heavy. This also makes them very robust, and are perfect for medium and larger-scale robots (no desktop rovers here - these sensors work well on robots the size of 24 VDC mobility chair bases and larger); for instance, if you look up Stanley from the Darpa Grand Challenge 2005 competition, you'll see five of the units facing forward on top of the vehicle. Each scans a line out many meters in front of the sensor, with a field-of-view (FOV) of about 180 degrees. It's like a radar sweep. As the platform vehicle moves forward, if the sensor is angled down, you can build up a height-map of the terrain in front of the platform. It is also possible to mount the sensor on a turntable to rotate it while it is oriented vertically, and scan a 3D volume, though at a much slower rate.

The other low-cost possibility is to purchase a surplus Neato robot vacuum LIDAR sensor. These units are also 2D, but use a parallax shift method of determining distance, kinda like explained here:

https://sites.google.com/site/todddanko/home/webcam_laser_ra...

Instead of a webcam, a 2D line-element imager is used. The whole contraption is then mounted on a turntable with a slip-ring system (for signals/power) to scan a 360 degree view around the sensor - the whitepaper behind the sensor can be found:

http://www.robotshop.com/media/files/PDF/revolds-whitepaper....

These sensors - as pulls or replacements - can be found on Ebay for about $100.00 USD each, and are much smaller (desktop rover sized), but have a limitation in that they don't work well outdoors (sunlight swamps the sensor) - but given the device they were meant to be used on, an indoor vacuum robot, that wasn't a concern.

Another option people have tried has been to get a low-cost 4-6 conductor slip-ring off Ebay (cheap), then build a similar motor-driven scanning system like the Neato lidar uses. For the actual sensor, a "LIDAR-Lite" module is used, which are relatively inexpensive (more than a Neato module, less than a SICK). They also have a longer range, and work well outdoors in sunlight. These have been mostly "homebrew" systems, so googling for such projects will be the best way to find them, but I've given enough info here that you probably won't need much hand-holding to implement something similar.

A recent off-the-shelf option that has become available, and is still fairly low-cost, is the Scanse Sweep:

http://scanse.io/

At a price of $350.00 USD, it isn't as cheap as a Neato sensor, but it does work better than that unit while still being small with longer distance capability, and is much cheaper than a new SICK LIDAR unit.

Finally, a form of LIDAR that is somewhat like a combination of computer vision coupled with lasers, this project has always been of interest to me:

http://www.seattlerobotics.org/encoder/200110/vision.htm

It is similar to the old webcam LIDAR I pointed out earlier, but uses a laser to create a line (cylindrical lens element), which by displacement viewed in the camera, and some simple trig, can lead to a form 2D and 3D scene reconstruction.

The original unit described used a standard NTSC camera and a basic detection circuit, but today one could potentially use a high-resolution web camera, and a laser pointer with a line diffraction grating, plus OpenCV to do the detection work. It is similar in principle to the simpler 3D turntable scanners out there used for 3D printing and model capture, if you need another example.

So - I guess all I can say is that if you are interested in this stuff, there are many ways to play with it today, without having to wait for future junkyard finds. While I agree that such sensors will be neat to play with, and will only come down further in price as they become more ubiquitous for manufacturers, you don't have to wait...