Proof the supports the 10 key max price

http://www.tf2outpost.com/trade/6433027 (Successful seller from the previous suggestion)

http://www.tf2outpost.com/trade/7274409 (C/O of ~9.5 keys in the form of an Unc. Juju)

http://www.tf2outpost.com/trade/6859180 (C/O of ~9-10 keys in the form of Crate 40 + 1 key)

Sellers for lower than current price

http://www.tf2outpost.com/trade/7090360 (8 keys + 2 ref)

http://www.tf2outpost.com/trade/7046144 (Sold for a Bills)

http://www.tf2outpost.com/trade/7053760 (9 keys + 1.33 ref)

http://www.tf2wh.com/item.php?id=828;1;2c183b46819be2ad0d7f8d170ac5dc0f (You can get it for the equivalent of 8ish keys)

Offers

http://www.tf2outpost.com/trade/6277658 (8 keys)

http://www.tf2outpost.com/trade/3725694 (8 keys)

http://www.tf2outpost.com/trade/6517375 (24 ref)

http://www.tf2outpost.com/trade/7145474 (Crate 40)

http://www.tf2outpost.com/trade/3693164 (V Lugermorph and another offer of 8 keys)

http://www.tf2outpost.com/trade/5465484 (Most recent is 8 keys, but there was a 9 key offer not too long ago)

http://www.tf2outpost.com/trade/4094944 (9 keys)

http://www.tf2outpost.com/trade/6622255 (9 keys)

Conclusion: I can't quite disprove the current price of 10 keys, since some people are still skimming close to it, but none of them exactly hit the mark. I'm adding a lower end to this again since the market for these things is just a tad bit lower at the moment, and it's possible to get them for below 10 keys. So 9 keys would be the most market-stable price in terms of offers and some sellers, while 10 keys is still able to be done, but with a bit of work, time and luck.