Sale #1:

http://www.tf2outpost.com/trade/26076069

Sold for a MN Tavish Degroot (19) + Level 1 Max (22 pure)

Seller:

http://backpack.tf/profiles/76561198043516452?time=1434870000 (June 21st)

http://backpack.tf/profiles/76561198043516452?time=1434956400 (June 22nd)

Buyer:

http://backpack.tf/profiles/76561198100811766?time=1434783600 (June 20th)

http://backpack.tf/profiles/76561198100811766?time=1434870000 (June 21st)

(19 * 0.9) + 22 = 39 keys

Sale #2:

http://www.tf2outpost.com/trade/26258174

Quick-sold for an Australium Grenade Launcher (18)

http://backpack.tf/profiles/76561198011162284?time=1434870000 (June 21st)

http://backpack.tf/profiles/76561198011162284?time=1435023835 (June 23rd)

18 keys with no overpay (check trade)

Sale #4:

http://www.tf2outpost.com/trade/26100204

Sold with 1 bud (3 pure) for a DBD Robo Modest

http://backpack.tf/profiles/76561198112764226?time=1433574000 (June 6th)

http://backpack.tf/profiles/76561198112764226?time=1433660400 (June 7th)

(45 * 0.9) - 3 = 37.5; rounded to 38 keys

Sale #5:

http://www.tf2outpost.com/trade/26032840

Sold for a Stormy Front Runner (26) + Strange Snack Attack (3) + 5 keys

http://backpack.tf/profiles/76561198133675785?time=1432450800 (May 24th)

http://backpack.tf/profiles/76561198133675785?time=1432623600 (May 26th)

((26 + 3) * 0.9) + 5 = 31 keys Seems to have sold fairly quick, probably fine to leave this out of the range.

Stormy Front Runner:

http://www.tf2outpost.com/trade/26239271 aaron is selling for 26 keys, sounds about right

Buyer sold it for these:

http://backpack.tf/profiles/76561198133675785?time=1432623600 (May 26th)

http://backpack.tf/profiles/76561198133675785?time=1432710000 (May 27th) - http://i.imgur.com/VhoGVar.png

Which is probably close to 26, as well.

Conclusion: sales are 18, 31, 38, and 39. 18 and 31 sold quick. 38-39 could be the range, but 38 flat looks nicer,and most other sales are lower so I'll be using the lower-end.