Gaiam Yoga Mat for $10.93.  Select free ship to-store for in-store pickup at REI.  Otherwise shipping is $5.99, making the total $16.92 shipped, or, shipping is free for REI members on orders over $75.00.  Here is a screenshot for your reference.  This yoga mat is made of plastic/rubber and is 0.125" thick.  The mat is available in Key Lime, Grape, Slate, and Sun Yellow.  Most places have it for about $21.