Asked Mindacos for advice on a range. He suggested 12 - 13.

Shock the Monkey.

http://backpack.tf/item/5436320806

Sale 1) Sold for 13 Keys

http://backpack.tf/profiles/76561198304138933#!/compare/1490486400/1490572800

http://backpack.tf/item/5273586685

Sale 2) Sold for 13 Keys

http://backpack.tf/profiles/76561198304138933#!/compare/1490140800/1490227200

http://backpack.tf/item/5264488186

Sale 3) Sold for 11 Keys

http://backpack.tf/profiles/76561198164651434#!/compare/1489708800/1489795200

http://backpack.tf/item/5262281874

Sale 4) Sold for an Aces Runner’s Warm-Up (14 Keys) + Burstchester (~3 Keys)

http://backpack.tf/profiles/76561198334066390#!/compare/1489881600/1489968000

14 + 3 = 17 Keys

Warm-Up Mini

http://backpack.tf/suggestion/591babe50e2cad55794ea22b - 14 Keys

Sale 5) Sold for an Orbiting Fire Professional’s Panama (12.5 Keys)

http://backpack.tf/profiles/76561198171659081#!/compare/1489881600/1489968000

Rounding to 13 Keys

Panama Mini

http://backpack.tf/suggestion/591b7fee0e2cad7dac7cfc76 - 12.5 Keys

Sale 6) Sold for a Duped Green Confetti Jeepcap (20 Keys) + ~1 Key of Items

http://backpack.tf/profiles/76561198309942981#!/compare/1489968000/1490054400

High Outlier.

Jeepcap Mini

http://backpack.tf/suggestion/590804e0e33877239231c9ab - 20 Keys

http://backpack.tf/item/5252601544

Sale 7) Sold for 12 Keys

http://backpack.tf/profiles/76561198312480435#!/compare/1489708800/1489795200

Sale 8) Sold for 10 Keys + ~3 Keys of Items

http://backpack.tf/profiles/76561198161149451#!/compare/1494201600/1494288000

10 + 3 = 13 Keys

http://backpack.tf/item/5252275500

Sale 9) Sold for 12 Keys + ~1 Key of Refined

http://backpack.tf/profiles/76561198048008254#!/compare/1489622400/1489708800

12 + 1 = 13 Keys

Sale 10) Sold for a Nuts and Bolts Soldier’s Slope Scopers (13.5 Keys)

http://backpack.tf/profiles/76561198087390671#!/compare/1489795200/1489881600

Rounding to 14 Keys

Sale 11) Sold for a Steaming Cosa Nostra Cap

http://backpack.tf/profiles/76561198079578383#!/compare/1489881600/1489968000

High Outlier.

http://backpack.tf/item/5246278220

Sale 12) Sold for 16 Keys

http://backpack.tf/profiles/76561197961309499#!/compare/1489881600/1489968000

http://backpack.tf/item/5229086945

Sale 13) Sold for 10 Keys

http://backpack.tf/profiles/76561198155183519#!/compare/1494028800/1494115200

http://backpack.tf/item/5219166369

Sale 14) Sold for a Strange Professional Killstreak Original (~10 Keys)

http://backpack.tf/profiles/76561198154136440#!/compare/1489276800/1489449600

Sale 15) Sold for an Aces Tin Capotain (11 Keys) + ~4 Keys of Items

http://backpack.tf/profiles/76561198002757046#!/compare/1489363200/1489449600

11 + 4 = 15 Keys

Sale 16) Sold + 2 Keys for a Steaming Powdered Practitioner

http://backpack.tf/profiles/76561198060690589#!/compare/1492646400/1493164800

High Outlier.

http://backpack.tf/item/5214131586

Sale 17) Sold for a Pro KS Aussie Wrench (~23 Keys)

http://backpack.tf/profiles/76561198090956917#!/compare/1492300800/1492387200

High Outlier.

http://backpack.tf/item/5208867526

Sale 18) Sold for 12 Keys + ~1 Key of Refined

http://backpack.tf/profiles/76561198344933095#!/compare/1489622400/1489708800

12 + 1 = 13 Keys

The sales at 10 and 11 are countered by the Buyers. The numerous Sellers in the 12 - 13 range support this.