Well, now I've "stolen" suggestions from two people. Go me!

http://backpack.tf/item/1134315532

Sale 1) Sold + 7.5 Keys of Items for a Dead Presidents Modest Pile of Hat (30 Keys)

http://backpack.tf/profiles/76561198053615186/#!/compare/1454659200/1454745600

30 - 7.5 = 22.5 Keys, which rounds to 23 Keys

The Modest was updated when the Sale occurred, so I'll use that price.

http://backpack.tf/item/502729596

Sale 2) Sold for an Orbiting Planets Armored Authority (22 Keys) + 4 Keys of Items = 26 Keys

http://backpack.tf/profiles/76561198086990597/#!/compare/1459468800/1459555200

http://imgur.com/nDs1tZt - Seller at 22 Keys