AMS Landscape Design Studios, Inc. The stone is a Travertine, and it is called 'Alanya Blend' with a 'Antique' finish (distressed / chiseled edge & unfilled).
The price (material only, not installed) is around $4 to $5 per square foot.
You can probably find a 'Walnut' Travertine for as low as $3 per sq. foot.
This material was purchased from Marmol Export (Anaheim, CA.).

Hope this helps you and good luck !

Drew Sivgals
AMS Landscape Design Studios, Inc.