Using last 2 months.

Sale 1:

Sold for 3 keys

https://backpack.tf/profiles/76561198421652838#!/compare/1703548800/1703635200

https://backpack.tf/profiles/76561198156334217#!/compare/1703548800/1703635200

https://backpack.tf/item/13008723496

= 3 keys

Sale 2:

Sold with negligible metal for 3 keys

https://backpack.tf/profiles/76561199111073161#!/compare/1703721600/1703808000

https://backpack.tf/profiles/76561198166908820#!/compare/1703721600/1703808000

https://backpack.tf/item/9634490765

= 3 keys

Sale 3:

Sold for 3 keys

https://backpack.tf/profiles/76561198251846986#!/compare/1703203200/1703289600

https://backpack.tf/profiles/76561199023521576#!/compare/1702512000/1703894400

https://backpack.tf/item/5639469719

= 3 keys

Sale 4:

Sold for 2 keys + 60 ref (~0.95 keys)

https://backpack.tf/profiles/76561199085308746#!/compare/1703721600/1703808000

https://backpack.tf/profiles/76561198061234620#!/compare/1703721600/1703808000

https://backpack.tf/item/6524972717

= ~2.95 keys

Other Sales:

#1

https://backpack.tf/profiles/76561198175279893#!/compare/1702252800/1705622400

https://backpack.tf/profiles/76561198850178158#!/compare/1704585600/1704672000

https://backpack.tf/item/12415487386

Untraceable, involves the Orbiting Fire Citizen Cane

#2

https://backpack.tf/profiles/76561198850178158#!/compare/1705276800/1705363200

https://backpack.tf/profiles/76561198803824764#!/compare/1705276800/1705449600

https://backpack.tf/item/12415487386

Untraceable

#3

https://backpack.tf/profiles/76561199064700653#!/compare/1702339200/1702425600

https://backpack.tf/profiles/76561198216241727#!/compare/1702252800/1702339200

https://backpack.tf/item/12295928007

Untraceable

#4

https://backpack.tf/profiles/76561198148983233#!/compare/1701302400/1701388800

https://backpack.tf/profiles/76561198033661509#!/compare/1702252800/1702684800

https://backpack.tf/item/11151452933

Untraceable, looks bulky.

#5

https://backpack.tf/profiles/76561198397843750#!/compare/1702857600/1703030400

https://backpack.tf/profiles/76561199139085248#!/compare/1702771200/1702857600

https://gladiator.tf/sales?item=Holy%20Grail%20Taunt:%20The%20Balloonibouncer&at=2023-12-18T07:28:37.659Z - labelled as 2 keys + 24 ref

https://backpack.tf/item/10998504523

Untraceable

#6

https://backpack.tf/profiles/76561199139085248#!/compare/1704758400/1704844800

https://backpack.tf/profiles/76561198421652838#!/compare/1704672000/1704758400

https://gladiator.tf/sales?item=Holy%20Grail%20Taunt:%20The%20Balloonibouncer&at=2024-01-10T07:29:46.874Z - labelled as 3 keys + 30 ref

https://backpack.tf/item/10998504523

Untraceable

#7

https://backpack.tf/profiles/76561198166908820#!/compare/1703808000/1703894400

https://backpack.tf/profiles/76561197974486633#!/compare/1679961600/1704844800

https://backpack.tf/item/9634490765

Untraceable. Gambled afterwards.

#8

https://backpack.tf/profiles/76561199026390261#!/compare/1700438400/1700524800

https://backpack.tf/profiles/76561198431561203#!/compare/1699401600/1701820800

https://backpack.tf/item/8825901811

Sold for Bloody Grip Balloonibouncer?

I feel like more would've been involved. Regardless, it should be used there if possible.

#9

https://backpack.tf/profiles/76561199107865875#!/compare/1704931200/1705017600

https://backpack.tf/profiles/76561199245733895#!/compare/1704844800/1704931200

https://gladiator.tf/sales?item=Holy%20Grail%20Taunt:%20The%20Balloonibouncer&at=2024-01-12T07:29:46.874Z - labelled as 3 keys + 30 ref

https://backpack.tf/item/7159186287

Untraceable. Appears to have sold to a gambler.

#10

https://backpack.tf/profiles/76561198870155636#!/compare/1700784000/1702252800

https://backpack.tf/profiles/76561199084784906#!/compare/1701561600/1701648000

https://backpack.tf/item/6606253806

Untraceable, 57 ref matches. No doubt it sold for 2 keys + 57 ref, with the keys going towards the Beams Shutterbug.

#11

https://backpack.tf/profiles/76561199084784906#!/compare/1703462400/1703548800

https://backpack.tf/profiles/76561199026390261#!/compare/1703462400/1703548800

https://backpack.tf/item/6606253806

Untraceable

#12

https://backpack.tf/profiles/76561199026390261#!/compare/1704326400/1704412800

https://backpack.tf/profiles/76561198273844579#!/compare/1703894400/1704499200

https://backpack.tf/item/6606253806

Untraceable, 2 keys match.

#13

https://backpack.tf/profiles/76561199084784906#!/compare/1703289600/1703376000

https://backpack.tf/profiles/76561199085308746#!/compare/1703289600/1703376000

https://backpack.tf/item/6524972717

Untraceable

#14

https://backpack.tf/profiles/76561199221395732#!/compare/1702684800/1705622400

https://backpack.tf/profiles/76561198850274253#!/compare/1702598400/1702684800

https://backpack.tf/item/5398791832

Untraceable

#15

https://backpack.tf/profiles/76561198850274253#!/compare/1704931200/1705017600

https://backpack.tf/profiles/76561199245733895#!/compare/1704931200/1705017600

https://backpack.tf/item/5398791832

Untraceable. Gambled afterwards.

#16

https://backpack.tf/profiles/76561199121394700 - no compare available

https://backpack.tf/profiles/76561199111073161#!/compare/1700524800/1700611200

https://backpack.tf/item/5025139216

Untraceable

#17

https://backpack.tf/profiles/76561199111073161#!/compare/1700611200/1700697600

https://backpack.tf/profiles/76561199061291714#!/compare/1700611200/1700697600

https://backpack.tf/item/5025139216

Untraceable. Gambled afterwards.

#18

https://backpack.tf/profiles/76561198258001464#!/compare/1704412800/1704585600

https://backpack.tf/profiles/76561198841279602#!/compare/1704499200/1704585600

https://backpack.tf/item/6478824418

Untraceable

#19

https://backpack.tf/profiles/76561198841279602#!/compare/1704844800/1704931200

https://backpack.tf/profiles/76561199069442401#!/compare/1704844800/1704931200

https://backpack.tf/item/6478824418

Untraceable

https://backpack.tf/item/5042335362 - scammers

Sellers:

https://imgur.com/a/YaY8mCr

https://backpack.tf/item/12415487386 - 4 keys

https://backpack.tf/item/10998504523 - 4 keys

https://backpack.tf/item/6362018135 - 5 keys

https://backpack.tf/item/6478824418 - marketplace

Sales at:

2.95

3 (3x)

There are also 2 gladiator sales at ~3.5 keys, but I'm not comfortable including them unless another one occurs at around that price. Looking into snapshots of listings shows several instances of this item being listed for below the suggested price here.

https://next.backpack.tf/classifieds/snapshots/Holy%20Grail%20Taunt:%20The%20Balloonibouncer/658c4732f628afb01d02cffd

https://imgur.com/a/7AI3JVD

That being said, I'll happily re-suggest if any of these ~3.5 key sales can be proven, or if we get a new higher sale.

Taking 2.95-3 keys.