Albert, their price is reasonable and plinth maker Lee Grage respond quickly on email. For example their kenwood style plinth for sp10 cost £400. Lee own his own workshop and he can make any custom plinth.
I got some info from Lee about his obsidian style plinths:
"We are offering a premium model version of this plinth, it's the same design but is 36mm thicker than standard and has a premium quality high gloss piano lacquer finish, this is a proper perfectly flat like glass lacquer and looks wonderful. It will also be available with more exotic veneers like Brazilian rosewood or Brazilian mahogany, bubinga if our supplier can supply us, just about any veneer is available. It will also be a little deeper with the top panel back bar being 1/2" thicker, it's substantially better."