I have been collecting #57 crates lately because i have a lot and I noticed that strongboxes are going for around .05-.11. But here's proof.

Sellers:

http://bazaar.tf/trade/739824 - 1 Scrap

http://bazaar.tf/trade/721996 - 1 Scrap

http://bazaar.tf/trade/705176 - 1 wep

http://bazaar.tf/trade/725634 - 1 scrap

http://bazaar.tf/trade/532823 - 1 wep

http://bazaar.tf/trade/730418 - 1 scrap

http://www.tf2outpost.com/trade/18761806 - 1 wep

http://www.tf2outpost.com/trade/18641835 - 1 scrap

http://www.tf2outpost.com/trade/18242425 - 1 wep

http://www.tf2outpost.com/trade/18679248 - 1 wep

http://www.tf2outpost.com/trade/18628011 - 1 scrap

http://www.tf2outpost.com/trade/18507544 - 1 scrap

http://www.tf2outpost.com/trade/18688080 - 1 scrap

http://www.tf2outpost.com/trade/18481736 - 1 scrap

http://www.tf2outpost.com/trade/18705373 - 1 scrap

http://www.tf2outpost.com/trade/18434700 - 1 scrap

http://www.tf2outpost.com/trade/18793703 - 1 scrap

Sold:

http://www.tf2outpost.com/trade/17894365 - 1 scrap, he's sold out.

http://www.tf2outpost.com/trade/18201281 - 1 wep each

http://www.tf2outpost.com/trade/17584911 - Sold 2 for 1 wep each

http://www.tf2outpost.com/trade/18019218 - 3 adds, 1 comment says that he bought four crates for 1 scrap, the others did not.

http://www.tf2outpost.com/trade/17806931 - 2 adds, guy bought 4 crates for 1 wep each, the other bought one

http://www.tf2outpost.com/trade/18187773 - sold 1 for a scrap

http://www.tf2outpost.com/trade/18517361 - 1 wep each

http://www.tf2outpost.com/trade/17822297 - 3 sold for a scrap each

http://www.tf2outpost.com/trade/18311094 - sold for a scrap

http://www.tf2outpost.com/trade/18566043 - 1 person bought for 1 scrap

http://www.tf2outpost.com/trade/18616124 - Sold for 1 scrap

http://www.tf2outpost.com/trade/18641539 - Added for strongbox for 1 scrap

http://www.tf2outpost.com/trade/18480764 - 2 different people bought for 1 wep each