https://backpack.tf/profiles/76561198394453476#!/compare/1594598400/1594684800 - 24 Keys for Pro KS

https://backpack.tf/profiles/76561198091267840#!/compare/1592438400/1593216000 - Strange Skull for Pro KS?

https://marketplace.tf/items/tf2/356;14 - Sold for $45.50 (24 Keys) and $54.99 (27 Keys)

https://marketplace.tf/items/tf2/356;14;kt-3 - Sold for $58.4 (31 Keys), $59 x2 (31 Keys), $40 (20 Keys), $30.15 (low), and $65 (high)

https://steamcommunity.com/market/listings/440/Collector%27s%20Conniver%27s%20Kunai - Sold for $49 (19 Keys, low)

https://steamcommunity.com/market/listings/440/Collector%27s%20Killstreak%20Conniver%27s%20Kunai - Sold for $40.25 (17 Keys, low)

https://imgur.com/a/RFrRTfX - Sellers at 24 Keys (has been 25 or less for 3 weeks), 30 Keys (has been 30 or less for ~3 months), and 35 Keys (2 months)

https://imgur.com/a/G2wScg7 - 24 seller was first listed at 25 Keys

https://imgur.com/a/R3sC0Jm - 30 seller was previously listed at 25 Keys to undercut another seller

https://backpack.tf/item/4130232688

https://backpack.tf/item/2822820831

https://backpack.tf/item/8314468789

https://marketplace.tf/items/tf2/356;14 - Seller at $47.50 (25 Keys)

https://backpack.tf/item/4243930932

https://marketplace.tf/items/tf2/356;14;kt-2 - Seller at $45 (24 Keys)

https://backpack.tf/item/3140645756

https://imgur.com/a/wOFyklB - Buyers at 19 Keys

https://backpack.tf/u/76561198810351708

https://backpack.tf/u/76561198259733876

https://backpack.tf/u/76561198454615761

https://backpack.tf/u/76561198342161127

https://backpack.tf/u/76561198862028218

https://backpack.tf/u/76561198928087066

The Pro KS sales are consistently higher than the regular sales, so I'd exclude them. That just gives sales at 24, 25, and 27.

I'd exclude 27 because of the multiple sellers for less (either currently or in the past). 24 - 25 will work here.