Sale 1:

Sold for 30 keys

Seller: https://backpack.tf/profiles/76561198064423172#!/compare/1522108800/1522281600

Buyer: https://backpack.tf/profiles/76561198046196261#!/compare/1521072000/1522454400

X = 30

Sale 2:

Nothing matches, but I guarantee that it sold for 30 keys

Seller: https://backpack.tf/profiles/76561198121326368#!/compare/1518566400/1518652800

Buyer: https://backpack.tf/profiles/76561198106868468#!/compare/1518566400/1518825600

X = 30

Sale 3:

Sold for 28 keys

Seller: https://backpack.tf/profiles/76561198313538268#!/compare/1521244800/1521331200

Buyer: https://backpack.tf/profiles/76561198076663295#!/compare/1520380800/1521763200

Bot.tf confirms: https://i.imgur.com/y3U3hAF.png

X = 28

Sale 4:

Sold for ~28 keys in items

http://www.tf2outpost.com/trade/29538618 - B/O of 26

Seller: https://backpack.tf/profiles/76561198179275509#!/compare/1517356800/1517443200

Buyer: https://backpack.tf/profiles/76561198060370171#!/compare/1517270400/1517443200

X = 26 (Capped by B/O)

Sale 5:

Sold for Stormy Storm Whirly Warrior

Seller: https://backpack.tf/profiles/76561198053747026#!/compare/1518825600/1518912000

Buyer: https://backpack.tf/profiles/76561198136944826#!/compare/1517356800/1518998400

Only sale on the Whirly, can be used on that instead.

Sale 6:

Sold for Power Surge Bubble Pipe + Strange Fed-Fightin’ Fedora (~2)

Seller: https://backpack.tf/profiles/76561198162282453#!/compare/1520812800/1520899200

Buyer: https://backpack.tf/profiles/76561198102810649#!/compare/1520640000/1520899200

Would rather have it used on the Bubble Pipe.

Sellers:

30 keys:

https://i.imgur.com/wZJ4KLl.png

https://backpack.tf/item/2407583627

Sales at:

26

28

30 (2x)

Going with 26-30.