9 month old price!

Sale 1:

Sold for 15 keys

http://www.tf2outpost.com/trade/26177514

Backpack of buyer:

http://backpack.tf/profiles/76561197967636876?time=1434178800 (June 13th)

http://backpack.tf/profiles/76561197967636876?time=1434265200 (June 14th)

Backpack of seller:

http://backpack.tf/profiles/76561198070789239?time=1434178800 (June 13th)

http://backpack.tf/profiles/76561198070789239?time=1434265200 (June 14th)

Sale 2:

Sold for Midnight Whirlwind Oblooterated (24.5*0.9) = 22.05 (rounding to 22 keys)

http://www.tf2outpost.com/trade/26092968

Backpack of buyer:

http://backpack.tf/profiles/76561198103187761?time=1433487600 (June 5th)

http://backpack.tf/profiles/76561198103187761?time=1433574000 (June 6th)

Backpack of seller:

http://backpack.tf/profiles/76561198161340716?time=1433401200 (June 4th)

http://backpack.tf/profiles/76561198161340716?time=1433487600 (June 5th)

Sale 3:

Sold for Cloud 9 Nanobalaclava (23.5*0.9) = 21.15 (rounding to 21 keys)

http://www.tf2outpost.com/trade/25735386

Backpack of buyer:

http://backpack.tf/profiles/76561198086129187?time=1429340400 (April 18th)

http://backpack.tf/profiles/76561198086129187?time=1429426800 (April 19th)

Backpack of seller:

http://backpack.tf/profiles/76561198158198662?time=1429340400 (April 18th)

http://backpack.tf/profiles/76561198158198662?time=1429426800 (April 19th)

Supportive-proof:

http://www.tf2outpost.com/trade/26092870 - Sold for Bubbling Milkman = <18 keys

http://www.tf2outpost.com/trade/25718309 - Sold for Dead Presidents Hound Dog = <18 keys

Notes:

No offers to indicate that Sale 1 is an outlier. On top of that, it took ~3 days to sell.

http://www.tf2outpost.com/trade/26230050 - B/O of 13 keys (gifted though)

http://www.tf2outpost.com/trade/26206890 - B/O of 18 keys

http://www.tf2outpost.com/trade/26177514 - B/O of 18 keys

http://www.tf2outpost.com/trade/26151297 - B/O of 20 keys

http://www.tf2outpost.com/trade/26176507 - B/O of 20 keys

Conclusion:

Three sales at 15, 22 and 21 keys. Because of the amount of sellers 20 keys or under, taking a conservative final range of 15-20 keys.

Feel free to support/counter my suggestion!