T. Foster wrote:But the issue with iron vs. steel isn't that it's "softer" (the way bronze is), it's just that it's more brittle and doesn't hold an edge as well, right?
Summon P&P
My impression is pure iron (rather then alloy) as well. As far as cost and avlblty, I suspect it would be somewhat rare (since its inferior as Foster points out) but not particularly expensive to have made, based on holy symbol costs: wood 7 sp, iron 2 gp (I'm assuming pure iron), silver 50 sp. A church might have iron weapons in storage for such problems and heroes suspecting demonic activity.
There is a movie Captain Kronos (Hammer) where certain vampires have to be killed with iron piercing the heart. He has his sidekick henchman hunchback professor buddy make one for him while he waits in some sort of drug induced meditation. He uses it in the battle and then after killing the vampire tosses it (likely as it has little value other then this completed task).

(Thats right Tony, thats the chick from Golden Voyage of Sinbad...

)
I believe another movie that featured iron as a way to kill an evil vampire like creature was Life Force (1985ish) Wheggie will remember this flick because it had some naked chick walking around sucking life energy out of googling guys. Then there was Quartermass and the Pit (70s Hammer) where a crane is pushed into the mass of a floating alien energy creature (if I remember correctly) the crane grounds it to the Earth effectively killing it. I have no idea where this idea of iron being used against evil things comes from (perhaps the idea of grounding)? Would be interesting to know. I'd only heard of silver in mythology.