I needed some limit switches for a project but didn't want to spend the $3-7 each that these things cost from Honeywell, etc. so I made my own using standard 6x6mm tactile switches. Buy the switches in bulk like I did and these will cost you about $0.05 each. Sure they're not the same level as the Honeywell but they'll get the job done.

Example tactile switches: http://goo.gl/ALffCi

Photo shows three that I made next to a Honeywell that I typically use. I soldered the leads after I glued the switches in so the solder job isn't the best. In the future I'll solder before I install the switch.

Note also that the dimensions on this may vary a bit printer to printer based on calibration. This is tuned for my printer, obviously, so you may need to tweak the file, or use some XActo action to get it dialed in for your situation. It's pretty close though and we're really only talking about, give or take, 1/2-1/4mm here or there. These are pretty small.