I was actually shocked at the price for these as well. $400 plus. However the owners explained as with everything else its for the testing and product liability insurance. That jacks up the cost.
I have used the anchors on standing seam roofs before but you have to be careful about sscratching on install/takeoff with some of them. and the ones that you tighten down to the roof in one spot still have to be taken off when your done instead of being able to walk back down the roof with them. Just my 2 cents though...