Comment by jseal for Here's a Poor man lidar, that could be used for mapping. It uses a sharp IR sensor and a servo.http://www.pirobot.org/blog/0014/The xv-11 laser is a fairly cheap setup for under $100 on eBay. http://wiki.ros.org/xv_11_laser_driver

I've done both suggestion second is better. I was never able to get a good map with the IR moving on a servo and my robot moving. Probably could have built a decent map if I had stitch several static maps together.