The Moto X was released today along with the Moto Maker customization tool. Moto Maker doesn't yet offer the option for a woodgrain back plate for the device, but we know that will be happening eventually. However, if you take a look at the Motorola website source code, it seems that the special back plate could cost you extra...
Source: http://www.phonearena.com/news/Motorola-website-source-code-suggests-a-wood-backed-Moto-X-could-cost-50-extra_id46716
Source: http://www.phonearena.com/news/Motorola-website-source-code-suggests-a-wood-backed-Moto-X-could-cost-50-extra_id46716