Reposting with fixed range, as per blind polar bear's suggestion.

http://www.tf2outpost.com/trade/14460691 B/O 2 buds

http://www.tf2outpost.com/trade/14697943 B/O 2 buds

http://www.tf2outpost.com/trade/14790229 B/O 2 buds

http://www.tf2outpost.com/trade/14821244 B/O 2 buds

http://www.tf2outpost.com/trade/10258908 selling 2 bubbles phantoms and a bubbles fez (1.5) for 5.5 buds - 5.5 - fez (1.5) = 4/2 = 2 buds each

http://www.tf2outpost.com/trade/13936588 B/O 2

http://www.tf2outpost.com/trade/12915593 B/O 2

http://www.tf2outpost.com/trade/9513012 B/O 2

The mass amount of B/Os at 2 leads me to believe the 2.1 high end is invalid. However, almost all of the trades with a B/O of 2 are unsold, leading to the low range:

http://www.tf2outpost.com/trade/12781916 was selling for 1 bud 11 keys

http://www.tf2outpost.com/trade/13942055 1 bud 16 keys (24th comment, not including sub-comments)

http://www.tf2outpost.com/trade/9764785 offered bubbles phantom for o. fire tree (1.7-2.2 back then)

Showing that, while not that common, people do sell it for less. The above 3 trades average out to about 1.8.