Cowboy does a cowboy hat suggestion.

Item 1: https://backpack.tf/item/15228620937

Sale 1: Untrace

https://backpack.tf/profiles/76561199017959799#!/compare/1751587200/1751846400

https://backpack.tf/profiles/76561198845761172#!/compare/1751068800/1751932800

Sale 2: Untrace

https://backpack.tf/profiles/76561198263112666#!/compare/1751673600/1751846400

https://backpack.tf/profiles/76561198845761172#!/compare/1751068800/1751846400

Item 2: https://backpack.tf/item/15233699084

Sale 1: Untrace

https://backpack.tf/profiles/76561199581722058#!/compare/1753747200/1753833600

https://backpack.tf/profiles/76561198254660352#!/compare/1753920000/1754352000

Item 3: https://backpack.tf/item/15351654800

Sale 1: Untrace

https://backpack.tf/profiles/76561198135388328#!/compare/1754092800/1754179200

https://backpack.tf/profiles/76561199474152483#!/compare/1752105600/1754784000

Sale 2: Untrace

https://backpack.tf/profiles/76561199474152483#!/compare/1756598400/1757635200

https://backpack.tf/profiles/76561198135388328#!/compare/1756598400/1757635200

Sale 3: Untrace

https://backpack.tf/profiles/76561198135388328#!/compare/1756684800/1756771200

https://backpack.tf/profiles/76561198226525604#!/compare/1756944000/1757030400

Sale 4: 30k pure

https://backpack.tf/profiles/76561198226525604#!/compare/1757030400/1757116800

https://backpack.tf/profiles/76561197971003538#!/compare/1757030400/1757116800

Item 4: https://backpack.tf/item/15291856081

Sale 1: Untrace, never shows up in seller's inv

https://backpack.tf/profiles/76561199013653880#!/compare/1752105600/1752192000

Item 5: https://backpack.tf/item/15910307702

Sale 1: Untrace

https://backpack.tf/profiles/76561198338666127#!/compare/1754611200/1754956800

https://backpack.tf/profiles/76561198935892417#!/compare/1753833600/1755043200

Item 6: https://backpack.tf/item/15493814571

Sale 1: BP buyout, put on marketplace

https://backpack.tf/profiles/76561198839782061#!/compare/1754092800/1755129600

https://backpack.tf/profiles/76561198244962432#!/compare/1754006400/1754092800

Item 7: https://backpack.tf/item/15446565482

Sale 1: Untrace

https://backpack.tf/profiles/76561198983856237#!/compare/1754179200/1754265600

https://backpack.tf/profiles/76561198316831771#!/compare/1754179200/1754265600

Item 8: https://backpack.tf/item/15364476140

Sale 1: Bulk

https://backpack.tf/profiles/76561198983856237#!/compare/1750896000/1750982400

https://backpack.tf/profiles/76561199046064612#!/compare/1750636800/1750982400

Sale 2: 27k pure, the 27k sale key at the top of seller's has keys coming from Unusual! :D / Unusual 4.0, and given that none of the outgoing keys share a history on buyer's side, but he did dump a Sylicone Succiduous Airdog and a Celestial Summit Airdog to Unusual 4.0, and a Steaming Flash of Inspiration to Unusual! :D, we can infer he used these to buy them. All dumped items with matching histories are linked below as supplementary proof.

https://backpack.tf/profiles/76561198836967499#!/compare/1754438400/1754524800

https://backpack.tf/profiles/76561199046064612#!/compare/1754438400/1754524800

https://backpack.tf/item/13759381755

https://backpack.tf/item/13316029532

https://backpack.tf/item/5791999089

Marketplace sales:

https://marketplace.tf/items/tf2/31514;5;u364

https://marketplace.tf/items/tf2/5021;6

$49.95, Jul 7th, key price for the day is $2.02, $49.95 / $2.02 = 24.72k

Classifieds link: https://imgur.com/a/eUJeKju

Sales at 24.72, 27, and 30 keys. Excluding the sale at 24.72, given the fluctuation of key price at the time, and it's proximity to buyers. Taking 27 and 30 keys as the low and high values for this.