Okay, let me interject...
The Emags are standard mag bodies(ULE or SS) with email rail and lowers. No eyes. Early ones has SS emag valves, later ones had X valves. An emag typically sells for 400-700 depending on the body/valve
The Xmags were very intricately milled and had swapable breaches and eyes and Xvalves. They typically run for over 1k in used condition. The Bone Daddy might be a tad high, but I'd still est it's value around $1600 or so.
The SLF's were made by Shocktech and there's estimated to be less than 50 in existence. They go for $2500+. The infection SLF was sold for $3500 not too long ago on AO.
