Center stone: 2.800ct(8.96 x 9.01 x 5.57mm), Round, F color, VVS2 Clarity, ID cut IGI-666402076
It is $855 for this ring semi mount without 2.8ct center in platinum. After 15% off, the price is $726.75.
original semi-mount price is $560.18, after 30% restocking fee, store credit is $392.13, so the price difference you'll need to pay is $334.62 (726.75 - 392.13).