The price needs an update. Proof is below. Easy no find it at 4 keys, nobody is willing to pay more.

http://www.tf2outpost.com/trade/9334917 - 4.5 keys, unsold, 1 day

http://www.tf2outpost.com/trade/9353473 - 4.5 keys, unsold, 1 day

http://www.tf2outpost.com/trade/9054771 - 4.2 keys (4 keys + 1,77 ref), unsold, 1 week

http://www.tf2outpost.com/trade/9193701 - 4 keys, unsold, 1 week

http://www.tf2outpost.com/trade/9239069 - 4 keys, unsold, 5 days

http://www.tf2outpost.com/trade/9340204 - 4 keys, unsold, 1 day

http://www.tf2outpost.com/trade/9377216 - 4 keys, 16 hours, no takers

http://www.tf2outpost.com/trade/9388152 - 4 keys, 2 hours, no takers

http://www.tf2outpost.com/trade/9374641 - sold for 4 keys

http://www.tf2outpost.com/trade/9199894 - sold for 4 keys

http://www.tf2outpost.com/trade/8918822 - sold for 4 keys

http://www.tf2outpost.com/trade/9168901 - sold for 3.5 keys

TF2Warehouse is selling it at 57225 credits (~ 4.5 keys), stock is full (nobody is willing to buy it for this price)

http://www.tf2wh.com/item.php?id=968;11;a5c48f7693cc3c003cb540d32cb8554c

Classfields: 2 at 4 keys, 1 at 3.75 keys (already sold, he doesn't have it in the BP)

http://backpack.tf/classifieds/search/Strange%20Gold%20Botkiller%20Knife%20Mk.II

Buyers:

http://www.tf2outpost.com/trade/9387566 - 4 keys in items, 3 hours, no takers

http://www.tf2outpost.com/trade/7730338 - 3 keys, 2 month, no takers