Sale #1:

[No Outpost trade]

Sold for 500 keys, or maybe very close to it anyways

Seller:

http://backpack.tf/profiles/76561198003539819?time=1434092400 (June 12th)

http://backpack.tf/profiles/76561198003539819?time=1434178800 (June 13th)

Buyer:

http://backpack.tf/profiles/76561198085272319?time=1433487600 (June 5th)

http://backpack.tf/profiles/76561198085272319?time=1434178800 (June 13th)

Only 440 keys tracked from the buyer's side, but there's also a bigger gap between dates meaning they probably got more keys between those 2 dates. I may add the buyer/seller later to confirm the trade unless someone else wants to. ^^

Sale #2:

http://www.tf2outpost.com/trade/26134965

Sold for a duped Scorching Modest + duped HOUWAR (~120) + duped Heart Guad

Buyer:

http://backpack.tf/profiles/76561198044871940?time=1433660400 (June 7th)

http://backpack.tf/profiles/76561198044871940?time=1433746800 (June 8th)

Seller:

http://backpack.tf/profiles/76561198060976608?time=1433660400 (June 7th)

http://backpack.tf/profiles/76561198060976608?time=1433746800 (June 8th)

Sale #3:

[No Outpost trade]

Sold for 323 keys + 50 ToD Tickets ~350 keys

Seller:

http://backpack.tf/profiles/76561198107740754?time=1430809200 (May 5th)

http://backpack.tf/profiles/76561198107740754?time=1430895600 (May 6th)

Buyer:

http://backpack.tf/profiles/76561198003539819?time=1430809200 (May 5th)

http://backpack.tf/profiles/76561198003539819?time=1430895600 (May 6th)

Sale #4:

Sold with many other items for a Burning Crone's

http://backpack.tf/profiles/76561198061374527?time=1430290800 (April 29th)

http://backpack.tf/profiles/76561198061374527?time=1430377200 (April 30th)

Sale #5:

Also another complex trade involving PE Crone's, PE DCO, and others

http://backpack.tf/profiles/76561198024925599?time=1430118000 (April 27th)

http://backpack.tf/profiles/76561198024925599?time=1430290800 (April 29th)

Sale #6:

http://www.tf2outpost.com/trade/25860696

Sold for Anti-Freeze Brainiac (288.5) + '72 Flippin (60.5) + Roboactive Western Wear (51.5) + Duped Searing Safe'n'Sound (25.5) + MN Luchadore (22.5) + Stormy Little Buddy (14.5) + 1 bud (~3.5)

Seller:

http://backpack.tf/profiles/76561198064824787?time=1430550000 (May 2nd)

http://backpack.tf/profiles/76561198064824787?time=1430636400 (May 3rd)

Buyer:

http://backpack.tf/profiles/76561198044871940?time=1430550000 (May 2nd)

http://backpack.tf/profiles/76561198044871940?time=1430636400 (May 3rd)

Items received: http://i.imgur.com/pLvJ0CH.png

Western Wear is outdated by 4 months, but has no recent usable sales. It shouldn't be too far off. http://www.tf2outpost.com/trade/26197104 Selling for 60 keys

(288.5 + 60.5 + 51.5 + 25.5 + 22.5 + 14.5 + 3.5) * 0.9 = 420 keys

Sale #7:

http://www.tf2outpost.com/trade/25781349

Sold for GBH Bonk Boy (195) + Sunbeams Soldier's Slope Scopers (135) + Stare From Beyond Smoking Skid Lid (50 pure) + Sunbeams Flipped Trilby (72.5)

Seller:

http://backpack.tf/profiles/76561198060511598?time=1430550000 (May 2nd)

http://backpack.tf/profiles/76561198060511598?time=1430636400 (May 3rd)

Buyer:

http://backpack.tf/profiles/76561198064824787?time=1430550000 (May 2nd)

http://backpack.tf/profiles/76561198064824787?time=1430636400 (May 3rd)

Items received: http://i.imgur.com/FEbwJxJ.png

Skid Lid is outdated, sold quick for 50 pure: http://www.tf2outpost.com/trade/25949511

(50) + ((195 + 135 + 50 + 72.5) * 0.9) = ~460 keys

Sale #8:

Involved in trade for a gold pan

http://backpack.tf/profiles/76561198060511598?time=1429772400 (April 23rd)

http://backpack.tf/profiles/76561198060511598?time=1429858800 (April 24th)

Sales are 350, 420, 460, and 500 (most recent). With 500 being the most recent sale, it's probably safe enough to leave 350 out of the range.