The others are right, you're not going to sell the 5820 for that price. The problem is that only enthusiasts are really looking at X99, and even then it's a very select few. Those that do almost universally go for the 5930 instead due to the 5820's limited PCIe lanes. X99 platform parts just aren't a fast seller unless you price very agressively. RAM being the only possible exception.
Heck Turtletrax had his X99 Deluxe listed very competitively for a long time here and I'm not sure he ever sold it.
Personally, I'd try starting at $420 and expect to settle for an offer just below $400, maybe you'll get $400 on the nose.
As for Crazyea and Vittra;..... WHY WOULDN'T YOU POST THAT IN THE HOT DEALS THREAD!?!?!?