Here's one for sale Ed: http://www.premium-militaria.de/product_info.php?info=p1794_Grabenlafette-MG-08-1-WK---NEW--.html" onclick="window.open(this.href);return false;
Hope tis helps you...
Not cheap indeed, but try to trace another one... in this case the price is really determined by the rarity of the piece and now it just depends on how eager you are to buy one... if you can find one...