Notes:

- All non-pure items are priced with backpack.tf.

- 5 known exist (hard to price due to low movement).

- Yes, I have one.

- This is my first second suggestion, have mercy! ;-) (repost due to incorrect range)

Not Sold:

http://www.tf2outpost.com/trade/2216611 (asking for 6 pure)

- [Denied] Cauldron Bubbles Hotrod [2.3-2.7 buds - 10key (.4buds) = 1.9-2.3 buds / 1.89 buds with median item rule ]

- [Retracted] Phosphorous Robo-glove [price not set, but a mid to higher-tier robo-effect 3-5 buds based on existing robo-glove robo-effects? / 3.6 buds with median item rule]

- [Retracted] 2.04 buds pure [supposedly acquired one from another seller for 'way more than 2buds']

Sold:

http://www.tf2outpost.com/trade/13159446 (4 pure b/o)

- [bought for green energy capotain (2-2.1 buds) + 13 keys (.6 buds) = 2.6-2.7 buds / 2.385 buds with median item rule]

http://www.tf2outpost.com/trade/11418593 (no b/o)

- [appears based on backpack.tf cache to have been traded for a hearts sultans (1.5-1.8buds) + 12 keys (0.54 buds) = 2.04-2.34 buds / 1.97 buds with median item rule]

Based on the above evidence, there is a trend (mean) of 2.1 - 2.3 buds pure with outliers in the high 2's/low 3's.