How are we FMVing metal from our stashes?

I'm planning on building some spring clamps for the S10, and dug out a 1/2"X1" steel bar out of my stash of metal from old projects.  It was originally 36" long, but is obviously shorter now.  Wondering how I FMV it?

1. At scrap price for what I use?  This seems a bit of a jerk move, as I didn't pull it from a scrap pile, I bought it at some point in the past.
2. At whatever cost I find for a 36" bar of steel, since that's what I originally bought?  Seems a bit extreme in the other way?
3. Find the cost of a 36" bar, and account for only what I use (probably about 16-18")?
4. Some other method?

I'm not building a top 10 car, and I don't feel like having a rule named after me, so I'm pretty flexible on how it should be accounted for, just want to make sure I follow along with what has generally been accepted in the past and don't step on anyone's toes.

In reply to eastsideTim :

Rules named after you aren't necessarily a bad thing. My rule is because I think I bitched the most about another team cheating the system. Plus I think I've turned it into a good thing. 

That said, I pay 99 cents a pound for steel cut offs at my local metal dealer. 

In reply to Stampie :

Hmm, I’ll make sure to weigh what I use just in case, and probably use that as the lowest vale I use, unless there’s more activity on this thread.

I pay 85 cents a pound for cutoffs.  

$0.60/lb here for drops. Go nuts.

Of the options listed...#3. Or go find some cheaper stuff, buy it and keep the receipt. Prorate the cost to the amount of the bar you use.