A finished prime rib roast sits on the grill. (Photo ©Chris Wilkins/Texas BBQ Posse) For me, nothing compares to cooking a prime rib roast on the grill. It’s a tasty cut of meat, always fun to prepare, and sometimes there can be a bit of adventure. And let’s not forget the cost. For this cook, we special ordered a four-bone, seven-pound rib roast from our neighborhood H-E-B in Austin, Tx. Price: About $85. Not a fortune, but certainly enough to keep the mind focused on proper preparation and technique, even after a glass or two of wine on a sunny…