The price is a bit outdated. Nobody is buying it at 5,5 keys anymore. Some people are willing to pay 5 keys, some sellers are willing to sell even cheaper. Proof is below.

Sellers:

http://www.tf2outpost.com/trade/8965236 - 5 keys + 1 ref (5.25 keys), unsold, 1 week

http://www.tf2outpost.com/trade/9083479 - 5 keys + sweets, unsold, 4 days (without bumps)

http://www.tf2outpost.com/trade/8783631 - 5 keys, unsold, 2 weeks

http://www.tf2outpost.com/trade/8909270 - 5 keys, unsold, 1 week

http://www.tf2outpost.com/trade/9157494 - 5 keys, unsold, 1 day

http://www.tf2outpost.com/trade/9174338 - 5 keys, unsold, 1 day (without bumps)

http://www.tf2outpost.com/trade/9169254 - 5 keys (willing to do 4 keys + sweets), unsold, 1 day

http://www.tf2outpost.com/trade/9004310 - sold for 5 keys

http://www.tf2outpost.com/trade/8812492 - sold for 5 keys

http://www.tf2outpost.com/trade/9169937 - sold for 5 keys

http://www.tf2outpost.com/trade/8910064 - sold for 4 keys + 2 ref (4.5 keys)

http://www.tf2outpost.com/trade/9133403 - sold for 4 keys + 1 ref (4.25 keys)

http://tf2tp.com/trade.php?trade=9215476 - sold for 4 keys

http://www.tf2outpost.com/trade/9177136 - sold for 4 keys

TF2Warehouse is selling it at 71495 credits (~5.5 keys). Stock level is 102% (overstocked)

http://www.tf2wh.com/item.php?id=967;11;9e9ef10dc8edb68ae105780c5b7304d0

Buyers:

http://www.tf2outpost.com/trade/8939707 - 5 keys, bought

http://www.tf2outpost.com/trade/7974248 - willing to pay 4 keys + 2 ref (4.5 keys), in comments

http://www.tf2outpost.com/trade/9065036 - bought one for 16 ref (4 keys)

http://www.tf2outpost.com/trade/9202747 - 3.5 keys, no takers

http://www.tf2outpost.com/trade/8245936 - 5 keys, inactive trade with a disabled autobump, doesn't have keys in his BP, got a lot of willing sellers