Well, They're $50 each because they have Tritium vials installed in the eye sockets. Tritium is expensive, and getting the vials imported into this country is extremely time-consuming because they have to pass through the approval of a federal agency (NRC?) due to their slightly radioactive nature. The particular federal agency has a prohibition on importing Tritium for what it considers to be novelty purposes (which is why glo-rings are so hard to get and don't have a U.S. distributor).
There are a few places to get pewter/silver/brass/copper skulls. I can give you the addy if you're interested.
As far as being an alternative, they glow all the time so some people feel they can better see their knives/lights/etc. in the dark with these skulls. Hope this helps.
-Anthony