I wanted to get one for a friend... and I can't seem to find any for 5.5.

Buyers buying for 5.5 keys (meaning it can be considered quicksell)

http://www.tf2outpost.com/trade/14361615

http://www.tf2outpost.com/trade/14375995

http://www.tf2outpost.com/trade/14414196

http://www.tf2outpost.com/trade/14366800

http://www.tf2outpost.com/trade/14388133

http://www.tf2outpost.com/trade/14420770

Sellers:

In Classifieds, cheapest one is higher than 6 keys:

http://backpack.tf/classifieds/search/id/52007438ba2536d515000007

In Outpost, knowing that people put higher prices, I try to focus on the offers:

http://www.tf2outpost.com/trade/14378725

http://www.tf2outpost.com/trade/14311388

http://www.tf2outpost.com/trade/14297051

http://www.tf2outpost.com/trade/14417096

http://www.tf2outpost.com/trade/14178400

http://www.tf2outpost.com/trade/14380000

All of them have people offering at most 6 keys + some ref.

Now, for the completed trades:

http://www.tf2outpost.com/trade/14402785 - 6 keys

http://www.tf2outpost.com/trade/14406199 - 6 keys, 1 ref

http://www.tf2outpost.com/trade/14401732 - 6.5 keys

http://www.tf2outpost.com/trade/14398976 - 6 keys

http://www.tf2outpost.com/trade/14400969 - 6 keys

http://www.tf2outpost.com/trade/14386976 - 6 keys

http://www.tf2outpost.com/trade/14384767 - 6.5 keys

http://www.tf2outpost.com/trade/14381744 - 7 keys *George Takei voice* Oh my!

Anyway, raising prices are hard, but I want to stress that 5.5 is quicksell, so it should be removed from the range.