Before I begin, I'd like to say "SUGGEST NEW PRICE BUTTON COME BACK TO YOUR ORIGINAL HOME!"

Now that's out of the way, theres two on the market.

http://www.tf2outpost.com/trade/8101942 - Very old prices, but 1 month ago, we have had an offer of 17 keys here. Also an offer of a Vintage Luger and a S F Nade Launcher (9+11 = 20 keys. Calling this 18 keys, due to a 10% overpay in items).

http://www.tf2outpost.com/trade/10759572 - wants 18 keys. Only offer is a lowball. worth 10 keys

CONCLUSION

Hard to reach a conclusion. I'm raising the low end to 15 even though there was no recent 15 key offers, but only because no offers of 12 or above have been done as of late. No unusual is worth less than 12, since there are HEAPS of people (Myself included) who relatively successfully buy unusuals at 12 keys.