First suggestion in a while

Sale 1 : Sold for Cloud 9 Grenadier's Softcap: ~ 24.5 x 0.9 = 22.05 > 22 keys

Histories:

http://backpack.tf/item/3432401165

http://backpack.tf/item/2352210787

Mini on Softcap:

Sold for Team Spirit Max's Head: ~ 24.5

Before: http://backpack.tf/profiles/76561198125849751?time=1432018800

After: http://backpack.tf/profiles/76561198125849751?time=1432278000

Histories:

http://backpack.tf/item/2352210787

http://backpack.tf/item/3128904006

By the looks of it he counted the max's head as pure so no overpay required:

http://www.tf2outpost.com/trade/25973181

Conclusion,

Being as this is the only Bone Dome I could find, and 2 out of the 3 sales on the history included a 2 for 1 trade, with the Bone Dome in the 2, this is the only single sale I could find.

Going with 22 keys.

Have a good day.