There aren't many options out there for low-cost 2D LIDAR systems. The difference in cost generally is due to a number of reasons; for instance, the expensive sensors you see out there can scan very quickly, spit the data out quickly, work well in a variety of lighting conditions (up to and including daylight), use high-quality optics and lasers (plus IR filters and other systems to remove noise caused by other IR sources that can drown out the laser light), and they also generally use a form of interferometry to calc the distance (basically, you modulate the beam with a wave in the GHz range, and compare the outgoing beam with the reflected version - the difference between the waves is proportional to the distance measured - but you need really high speed timer circuitry for this). Some high-end sensors (so called LIDAR cameras) use time-of-flight and special high-speed optical sensors and timers to measure the time it takes from laser emission to reception of the reflected beam.
All of that adds up to dollars. Every other low-cost method (including "real" - vs cheap "ultrasonic" - laser distance measuring devices) uses triangulation to measure the distance. You have a laser, then you have a sensor - usually a linear CCD or similar array, and the baseline between the two is known; using this information and some simple trig, you can calculate how far away an object the laser reflects off is by where the beam is detected on the linear array.
This method suffers from low accuracy (because you can only get so many pixels in a linear array), and the need for the device to be manufactured fairly well so that the sensor can "see" what the laser is aimed at. Even so, it tends to be a cheap way to implement a range finder. That said, here's a breakdown:
- A SICK, Hokuyo (or other expensive vendor) 2D LIDAR (~ $1000.00+ USD, depending on how you source it)
- Ripping the sensor out of a Neato XV-11 vacuum cleaner robot and "hacking it" (~$400.00 USD)
- The Parallax 1D LIDAR sensor (~$130.00 USD) - mount on a servo to pan it, for 2D sensing (somewhat slow)
- Homebrew (??? USD)
Item 1 is basically out of most people's budget; you've already indicated it isn't for you (but hey - I have seen sensors of this nature, in used condition, go for as low as $800.00 on Ebay - so maybe you might consider it if you want something much better). Likely - item 2 will be your best bet; there are a few sites out there that detail how to "hack" these and use them with an Arduino and/or other microcontrollers. You basically do some simple serial comms with them, and they spit out an approximate "360 degree" measurement list; whether the sensor works well in daylight is unknown (but I would guess: not very likely).
Item 3 is a good deal because it basically does what most homebrew systems do - via a "parallax" method as described above, and does the processing of distance measured and such on-board, so you don't have to do much to interface to it. Add a nice servo to pan it around (mount it with the long-axis "up" to keep the servo mass down), and you can have a nice and fairly fast 2D LIDAR system (certainly at least as fast as an ultrasonic sensor with the NewPing library - but probably much faster is possible).
Lastly - Item 4 - homebrew - is an option. What you are suggesting with the serial communications system is certainly possible; I would see if the serial output is already in some TTL serial (5V or 3.3V) format, first (instead of going through a special interface cable). How fast you can make those measurements, though, would be a question to find out about.
Or - you can go "true homebrew" - here's a couple of ways of doing it - the first requires a PC and a webcam, the second can be done (in theory) with an Arduino or similar, but is not for the faint of heart, and the third can definitely be done with an Arduino. All use variations on the parallax geometry measurement methodology, in different forms (the second being the most complex - while the third is interesting in that it scans the laser, and keep the single phototransistor stationary - in effect, giving you a virtual linear "ccd" array):
A Real-time Laser Range Finder (you may have to refresh this one a couple of times to get it to fully load all the images)
http://letsmakerobots.com/node/2651
Hope these links help - I've answered this question so many times, and nothing has really changed much over the last couple of years; I think I am going to make a post of this on my web site, just so I can point there in the future...