I own 2 g. boonies so I'm glad someone else made this suggestion (I got them for 3 keys each). They are scarce, and enough people who go looking for one seem willing to pay 3 keys. I could only find one seller that might go for under 3 keys, but in the past I've seen 3 key offers. Also I remember that guy looking to buy for 6 keys, I think he was desperate.

http://www.tf2outpost.com/trade/4515852 (under 3 keys, recently put up)

http://www.tf2outpost.com/trade/4247489 (sold for 3 keys)

http://www.tf2outpost.com/trade/3936514 (personally sold for 3 keys)

http://www.tf2outpost.com/trade/4043352

http://www.tf2outpost.com/trade/4415095

Consistently getting offers of around 3 keys.

6 on Outpost btw.