Hey, firstly:

1 Key = 8.33

0.4 Keys = 3.33 ref

0.5 Keys = 4.11 ref

0.6 Keys = 5.00 ref

0.7 Keys = 5.88 ref

0.8 Keys = 6.66 ref

Etc.

Classifieds:

http://backpack.tf/classifieds/search_redirect?appid=440&defindex=1085&quality=11&tradable=1&craftable=1

3.0 Keys:

http://www.tf2outpost.com/trade/19982311 - never been bumped

http://www.tf2outpost.com/trade/19972088 - sold

3.1 Keys:

http://www.tf2outpost.com/trade/20059733 - young

3.4 Keys:

http://www.tf2outpost.com/trade/20065349 - young (that info)

http://www.tf2outpost.com/trade/20070520 - young

http://www.tf2outpost.com/trade/20040657 - 2 days

3.5 Keys:

http://www.tf2outpost.com/trade/19993600 - sold

http://www.tf2outpost.com/trade/20064864 - young

http://www.tf2outpost.com/trade/19844753 - poorly bumped

http://www.tf2outpost.com/trade/20053623 - 1 day

http://www.tf2outpost.com/trade/20041017 - 2 days

http://www.tf2outpost.com/trade/19858681 - 1 week

http://www.tf2outpost.com/trade/19931670 - 1 week

http://www.tf2outpost.com/trade/19822492 - 1 week

http://www.tf2outpost.com/trade/19658247 - 3 weeks

3.6 Keys:

http://www.tf2outpost.com/trade/20000542 - sold after 2 days

http://www.tf2outpost.com/trade/19998145 - 4 days

http://www.tf2outpost.com/trade/19939575 - 1week

http://www.tf2outpost.com/trade/19798883 - 2 weeks

3.7 Keys:

http://www.tf2outpost.com/trade/19963643 - sold

http://www.tf2outpost.com/trade/20072103 - spec ks - young

http://www.tf2outpost.com/trade/20059733 - 1 day

http://www.tf2outpost.com/trade/19905746 - 1 week

http://www.tf2outpost.com/trade/19685420 - 3 weeks

3.8 Keys:

http://www.tf2outpost.com/trade/20013353 - sold

http://www.tf2outpost.com/trade/20049505 - spec ks

http://www.tf2outpost.com/trade/20001374 - 4 days

http://www.tf2outpost.com/trade/19953340 - 6 days

http://www.tf2outpost.com/trade/19901888 - 1 week

http://www.tf2outpost.com/trade/19845534 - 1 week

http://www.tf2outpost.com/trade/19317089 - 1 month ?

Sorry about hardly any solds didnt have time to go through trade.tf yet this is only outpost.. will do in an hour :) thanks!