Sale 1:

http://www.tf2outpost.com/trade/25147575b

backpack before: http://backpack.tf/profiles/76561198040116461?time=1424764800

backpack after: http://backpack.tf/profiles/76561198040116461?time=1424851200

Sold for a bud + 3 keys

1.25 rounded up to

1.3 buds

Sale 2:

http://www.tf2outpost.com/trade/25148901#latest

Proof: http://postimg.org/image/phb8kq2q1/

Kill-a-watt Toy Soldier + The ebenezer (1 key) + Genuine Brimstone (2 ref) for Vintage Professional Killstreak Gunslinger (6.5) + Larrikin Robin Circling Peace Sign (1.1)

x + 0.094 = 0.9 (1.64)

x = 1.38 rounded up to

1.4 buds

Vintage Professional Killstreak Gunslinger mini: http://steamcommunity.com/market/listings/440/Vintage%20Professional%20Killstreak%20Gunslinger

13.5- 14 euros seems to be the most common selling point thus taking as 6.5 keys