"We will set your diamond in a platinum prong and 18 karat gold "Tiffany" style solitaire mounting, at no additional cost. An all-platinum mounting is also complimentary with diamonds costing over $6000. Browse the different mounting styles we offer at the Engagement Rings page. Compare what others might charge for these mountings."
Cost of a platinum setting on Blue Nile
Six-Prong Ring in Platinum This six-prong platinum setting is designed to beautifully complement your choice of center diamond. $570
Doesn't sound like such a great deal for spending 6k!