Looks like grade B's are going for high 5's and grade A's are going for mid/upper 6's to $700 to me.
HKParts sell great products, at full retail prices. I have ordered from them and their service is excellent. I've found some of the products they sell at better prices though, sometimes by hundreds of dollars.
Anything HK you are going to pay for though.
Last HK part I bought was a UMP FBI lower for my USC conversion. HKParts wanted over $400 dollars for theirs. I found it at HKSpecialists for less than $290.