Why do you want them?
* Shock padding for your feet/body.
* Insulation between you and the cold concrete.
* Easy to clean.
* Easy to assemble and move at need.
* Cheap enough to be disposable after a few years.

I have enough of these mats to cover my garage floor.
I try to catch them on clearance at warehouse stores..

The following links are examples of the mats I use.

http://www.greatmats.com/products/dense-foam-mats-exercise.php

http://www.getrung.com/google.html?gclid=COSvi567v58CFQTyDAodlUG_4Q