Let's start off by noting there are only 25 according to link #1. There is only one on tf2op and google did not help me find this variant of the cowl elsewhere. We will focus on the previous trades this Cowl has been in.

#2 shows offer of 14 ref and level 42 Team Captain ("whoa dude"). This could be considered 8-10 keys. We've got another collector (and seller) offering 15 keys. He later offers a 1:1 with an uncraftable Hetman's- another rare uncraft. Two other collectors offer uncraftable Brain Buckets 1:1. This makes it seem like the Cowl is the more sought after and perhaps more valuable than those. We wrap it up with a 1 bud offer that the seller accepts without any hesitation. Someone else offers 2 Buds- doubling the last offer. None of these came to fruition accepted but we can determine that the seller would have taken a Buds easily.

#3 is the current trade for the cowl. Rejects offer of #69 Russian Rocketeer less 6 keys in sweets(user bought this for 20 keys + gift wrap, he's currently accepting offer of Borderlands 2 which is about 35-40 keys. Backpack.tf suggests the Rocketeer at 2-2 Buds, not sure how it determines that.). Same user offers an S.F. Sniper Rifle (24-25 keys) User mentions the seller would need to add sweets but it's not sure if he means only if trading for his UC UT Planeswalker set (current offer on that set is an uncraft Lumbricus Lid)

Despite what the Rocketeer is being sold for (don't think the owner of the Cowl figured he could get much for it), the best offer right now seems to be the Strange Festive Sniper Rifle. Given that, and the fact that owner was willing to sell for a Buds 3 months ago, I've come up with the current price suggestion.

If anyone has any information or suggestions for a better price, let me know. I don't mind removing this one and adding another.

@Gwynn

It's hard to argue over the importance of a "piece of text" when, in the end, we're talking about a "grouping of pixels".

Also the rarity of Diamond Botkillers cannot really be compared to rare uncrafts. Diamond Botkillers are still obtainable, increasing in number every few days, but the Uncraftable Cowls can no longer be obtained. New doesn't necessarily mean rare, it means NEW.

Also I would argue against diamond botkiller weapons as being "original". They're different colored versions of the silver and gold ones we've gotten used to. Those also are just reskins of stock weapons. Not to mention that a lot of people hate the "jiggle bones" skull attachments, citing them as being "lazily attached".