I plan to buy a mounting at store in Chicago and buy a loose diamond via the internet. The mounting is 6 prong platinum for a 1.2 carrot stone (it already has two pear shape stones on the sides). If I pay the full retail price of the setting (around $2,000) is it reasonable to get the stone mounted for free since I paid full price or how much should I expect for the mounting price since it isn't their diamond?