The textures are differentiated by their resolution:
128x128 Low Resolution
256x256 Medium Resolution
512x512 High Resolution
The higher the resolution, the greater the amount of details and space to develop the texture its owner will have, and because of this, the price increases. Market prices are constantly changing due to "demand and provision" process, so don't be alarmed by this.
Last edited by Larm; Jun 21, 2014 at 05:27 AM.