Sale 1: 79.99 USD on mp.tf; 1 key = 1.99 USD --> 40 keys

https://marketplace.tf/items/315;5;u32

https://backpack.tf/item/736675791

Sale 2: 80 USD on mp.tf; 1 key = 1.92 USD ---> 41.6; rounding to 42 keys

https://marketplace.tf/items/315;5;u32

Sale 3: 32 keys pure

https://backpack.tf/profiles/76561198304138933#!/compare/1525305600/1525392000

Sale 4: Sold for Vivid Plasma Prussian Pickelhaube + Nuts n' Bolts Engineer's Cap + ~3.5 keys in items

https://backpack.tf/profiles/76561198040425824#!/compare/1522972800/1526774400

https://backpack.tf/profiles/76561198040603999#!/compare/1525392000/1525478400

Can be used on Pickelhaube

Sale 5: Quicksold (same day)

https://backpack.tf/profiles/76561198032636421#!/compare/1527292800/1527379200

Sale 6: Untraceable

https://backpack.tf/profiles/76561198045466865#!/compare/1529107200/1529193600

Matured seller at 35; buyers at 27.

Recent sales at 40, 42; sale at 32.

Suggesting range from 32 to 42. https://i.imgur.com/mntwOkj.png