You need to be strong to carry this heavy crate

Sellers:

http://www.tf2outpost.com/trade/26107892 - 12 Keys -> 4 Months

http://www.tf2outpost.com/trade/26959439 - 6 Keys -> 1 Month

http://www.tf2outpost.com/trade/27110830 - 5 Keys -> 2 Weeks

http://www.tf2outpost.com/trade/26289086 - 5 Keys -> 3 Months

http://www.tf2outpost.com/trade/27211241 - 4 Keys - Young (mine)

From previous suggestion - http://www.tf2outpost.com/trade/27092089 - Lost on sweetstakes - http://backpack.tf/item/3181757316

Classifieds:

http://imgur.com/a/L4dew

x3 4 Keys

x2 5 Keys

x2 6 Keys

Conclusion:

Can't sell at 5 Keys+ being unsold for weeks or even months. 3 Sellers at 4 Keys on the classifieds, which should be valid enough for an item such as this, one being unsold for 3 Days. SCM supports a drop. Taking a flat range of 4 Keys.