OK, I probably misread the tone in your first sentence.
It's easy to guess! Nearly impossible to guess accurately, though, I agree.
You're right about it being less than 1% of the total, although I disagree that this makes the estimate absurd. I think it's entirely possible that the gold 5S constitutes less than 1% of production or sales so far. I certainly could be wrong.
The under supply can't be too bad though - I just checked on eBay, and 16gb gold iPhones are going for around $1000. You can buy a TMobile contract free for $650 online through the Apple Store. That's only a 50% markup...
Man, does eBay's search ever suck. I specify gold, 5S, unlocked, and it still gives me all sorts of irrelevant listings.
Looks like the typical price is around there, though. I do see some sold for well over $2,000, though. I wonder if that means the $1,000 listings are underpriced, or if those high-end listings just got lucky and found a few suckers.
Just pointing out that it is impossible to guess, and that your last number constitutes less than 1% of the total estimated iPhone 5Ss sold.