LIDAR from a Neato vacuum cleaner is another option if you are open to other ideas. If you Google or eBay or Amazon the terms "neato lidar" you will see what I am thinking of. Here is a link to some on eBay. Some vendors even offer code and instructions on how to talk to these devices.
http://www.ebay.com/sch/i.html?_from...dar&_sac at=0
-Hugh