I tried to do this a few days ago, but sales were all over the place. Now there are two more sales, one usable, and it's higher than 43:

Most likely sold with 12 keys for a Cloudy Moon Private Eye (78)

http://backpack.tf/profiles/76561198079504588#!/compare/1474156800/1474243200

http://backpack.tf/profiles/76561198085365560#!/compare/1474156800/1474243200

Probably sold with 10 keys for a Cloudy Moon Whoopee (77.5)

http://backpack.tf/profiles/76561198079504588#!/compare/1474416000/1474502400

http://backpack.tf/profiles/76561198071103112#!/compare/1474416000/1474502400

Bulk for a duped Misty Skull Ushanka.

http://backpack.tf/profiles/76561198016070169#!/compare/1474416000/1474502400

You should probably cap the higher sales at 55 (two sellers in classies right now) and go with 43-55 or something like that, because 43 flat might be low.

All sellers are 50+ http://imgur.com/a/0UtdO This guy got low balled. Why base price off one low ball sale. He discounted it like 25 keys. really?

there was just a seller at 53-56. they posted suggestion

http://backpack.tf/profiles/76561198142191905#!/compare/1475712000/1475971200

Another sale ~54.5.

A range is probably needed here.