Have you tries purse.io? This is exactly what they are for and can get you 20%+ off.
https://app.purse.io/product/B001VDE984 $4341.50
$4570.00 Save $228.50 (5%)
I am pretty certain I can go to a jewelry store and get it for around 4200
You can post an offer for more than 5% and wait for someone to fulfill it. Usually at 25% I will get someone to buy it within a day or two, may be a bit longer for such a high dollar value item.