After being pointed out by the mods my previous suggestion needed minis and a slight tweaking of a price range. So here is the updated / re-suggest version

Sale #1

Bought it for Australium Scattergun (worth 24 keys) + 18 keys pure + strange virtual viewfinder worth roughly 1.1 key

proof: https://imgur.com/a/gg9PVTc

43 keys in total. (The Aussie may be considered pure)

In this trade the Bandana was gifted to go together with the loadout but for the sake of suggestion I will count this in to the trade. - Rounding it to 42 keys

Sale #2

Disco Beat Down Tartan Tyrolean (worth around 26 keys at the time and still is) + 17 keys pure

proof:

I politely asked the seller to provide me with the screenshot of his trade when he bought the hat

https://steamuserimages-a.akamaihd.net/ugc/965348817766906205/BF71280B116A2F90A2A6109C50B9EFDE47669340/

and here is the backpack comparison to clear things up a bit.

https://backpack.tf/profiles/76561198110834357#!/compare/1535155200/1536364800

Here is a mini for The DBD Tartan Tyrolean (Credits to Randy):

Sold for a Steaming Samur Eye(9) + O.F Ol'Geezer (mini below) + 3 key item = 24 Keys

https://backpack.tf/profiles/76561198032016356#!/compare/1532476800/1532563200

Additional Geezer Mini

Sold for 12 keys + some ref - round down to 12

https://backpack.tf/profiles/76561198123224716#!/compare/1533427200/1533686400

Seller for 12 keys - https://i.imgur.com/uoM1kCy.png

Taking 12 as mini

Second sale taking 41

----------------------------------------------------------------------

(Credits to Erik)

Sold for a C.Heart Chieftains + 1 key item = chief is 2 years outdated, could use there maybe

https://backpack.tf/profiles/76561198111608504#!/compare/1534118400/1534291200

Sale #3

Marketplace sale sold for 43 keys

85$ , keys were 1.98 = 43 Keys

https://marketplace.tf/items/417;5;u70

http://manic.tf/keyprice/?at=2018-07-04

Sale #1 42 keys

Sale #2 41 keys

Sale #3 43 keys

Re-suggested for a price range 41 - 43