your range is as wide as you say, so lets look at the sales like this:

36 - went to a quickbuyer

46 - nov 8 MP sale $83.30

48 - gladiator.tf buy order

56 - pure

57 - dec 8 MP $100

61 - dec 10 MP, $109.99

62 - dec 3 MP sale $109.99

66 - nov 28 sale $115.99

75 - november 4 MP, $136

80 - gladiator stats

82 - october 11 MP, $152.99

https://backpack.tf/item/8878688917

This is the gladiator stats sales

so that means 48 1 ref went to a buy order and 80 was sold by the bot

https://backpack.tf/profiles/76561199098607786#!/compare/1607990400/1608163200

https://backpack.tf/profiles/76561198123146104#!/compare/1608076800/1608163200

keys do leave the 2nd compare, but unless you can get a screenshot to prove it sold for 80 keys (as the compares do not show it), then you cant say it was 80 keys

let me show you why:

https://gyazo.com/7ca81ce249c4203e2319ed6f7d281b58

https://gladiator.tf/sales?item=Misty%20Skull%20Sultan%27s%20Ceremonial

i sold this through my bot, glad stats says 100 keys

https://gyazo.com/677629dec3513838e0498b18e3572da3

but it didnt actually sell for 100 keys, it sold for items

glad stats only remember the buyout and that it sold, not necessarily that it sold for the exact price listed

so with this, the 80 key sale is nothing until you can prove it (and even if you can prove it, the rest of the reasoning below will let you exclude it anyway)

now for the rest of the sales

36 went to a quickbuyer

46 is low because of buyers

and 48 was a buy order, so we can count those three out

pure sales have more precedence over MP sales because a BP price represents the pure value of the item - therefore a pure sale is much more accurate in representing the value than say, an MP or item sale

75 and 82 are both MP sales from over 2 months ago - and they are at $153 and $136

in comparison, all of the sales past that are all lower than those sales, so we can hypothetically take a 2 month timespan instead of a 3 month timespan here

if it were me, i would go with 56-66 keys, cutting off 36-48 because they are low/to buyers

and cutting off 75-82 because 80 is unconfirmed and 75/82 are older and have many sales under it on the same medium (marketplace)