10 keys seems to be the average selling price on Outpost now.

10 keys

http://www.tf2outpost.com/trade/18350968 - Sold after 1 week.

http://www.tf2outpost.com/trade/17978513 - Will bow down to 10 keys. (Read comments.)

http://www.tf2outpost.com/trade/18407645 - Unsold for 5 days.

http://www.tf2outpost.com/trade/18502744 - Unsold for 1 day.

10 - 11 keys

http://www.tf2outpost.com/trade/18451613 - 10 keys and 4 ref. Unsold for 3 days.

http://www.tf2outpost.com/trade/18517144 - 11 keys. Young.

http://www.tf2outpost.com/trade/18458102 - 11 keys. Unsold for 3 days. Under-bumped.

12 keys:

http://www.tf2outpost.com/trade/18404014 - Unsold for 5 days.

Buyers:

http://www.tf2outpost.com/trade/18399445 - Pink Bills w/ Halloween Spells (7 keys?) + Pink Graybanns (1.6 keys) + Tuxxy (3 ref) + G. Shred Alert (2 keys) + G. Champ Stamp (4 ref) + Specialised Killstreak Original (?) = 11.6+ keys. This trade got snatched very quickly proving that 12 as part of the price is out of the question.

Possible counter-proof debunked:

http://www.tf2outpost.com/trade/18435201 - Seems to have been sold for nothing?

http://backpack.tf/profiles/76561198055052984?time=1394006400 - From time of buying.

At least less than 12 keys though (maybe 10?) as Brakkit is selling for 10 keys 3 ref soon after the above trade got closed.

Intelligent and structured criticism would be appreciated as I am still quite new to making price suggestions. Thank you! :D

Should be enough considering the amount of proof in previous accepted suggestions with only 2 or 3 links. Any other proof (or counter-proof) is welcome. :)