I was the first bidder for that MR556 and had been watching that auction closely. It had been sitting at $2,900 for several days.Supply & Demand mixed with a little gun control.... In Box New H&K MR556A1 : Semi Auto Rifles at GunBroker.com
Perhaps the highest I've seen them go for: $3,325.
This MR556 is in California, and it will be interesting to see what the market brings for that one.
I picked up a barely used BB date code MR556 in Dallas this weekend for $2,600. I was very happy to be able to shop locally and skip Gunbroker for that one.