Couple new sales since the current suggestion went up, I'd like to add them to it.

Sale 1: 48 keys

48 pure

http://www.tf2outpost.com/trade/27410680

Sale 2: 51.3 keys

Vivid Plasma Vintage Tyrolean (50) + Strange Haunted beep boy (7)

I offered

http://imgur.com/a/BnL9k

(50 + 7) * .9 = 51.3

Sale 3: ???

Stare from beyond cloud crasher

before: http://backpack.tf/profiles/76561198085686974?time=1450684800

after: http://backpack.tf/profiles/76561198085686974?time=1450771200

cloud crasher is outdated, can't find any sales

Sale 4: ???

bulk trade

http://backpack.tf/profiles/76561198024703004?time=1446969600&compare=1447574400

Credit to Nos for sales 1 and 4, sorry for taking them but the suggestion isn't accurate anymore

Mini on outdated tyrolean: 50 keys

1:1 with Cauldron Bubbles Das Ubersternmann, neither of us offered.

Before: http://backpack.tf/profiles/76561198115974835?time=1449993600

After: http://backpack.tf/profiles/76561198115974835?time=1450166400

also

seller currently selling at 50 keys

Taking 48 as low end from sale and current seller at 48.

Taking 51 as high end from 51.3 sale rounded down.