1 year old price!

Sale 1: (outlier)

Sold for 1 bud and an Australium Tomislav (buds were 8 keys)

8 + 9 = 17 keys

No outpost trade

Seller Before: http://backpack.tf/profiles/76561197996732143?time=1427439600

Seller After: http://backpack.tf/profiles/76561197996732143?time=1427785200

Sale 2:

Sold with a bud for a max’s (buds were 11 keys, max’s were 35.5)

(35.5 - 1) -11 = 24.5 keys rounding to 25 keys

http://www.tf2outpost.com/trade/25323504

Seller Before: http://backpack.tf/profiles/76561198119662522?time=1426230000

Seller After: http://backpack.tf/profiles/76561198119662522?time=1426316400

Sale 3:

Sold with 3 keys for a Stormy Storm Master's Yellow Belt

(29*0.9) - 3 = 23.1 rounding to 23 keys

http://www.tf2outpost.com/trade/25779668

Seller Before: http://backpack.tf/profiles/76561198049761080?time=1428649200

Seller After: http://backpack.tf/profiles/76561198049761080?time=1428735600

Conclusion:

Sales at 25, 17 and 23. Taking the final range at 23 to 25 keys.