A hat's value should be valued on a case by case basis, depending on the market's supply & demand.
It should not be based directly off a website's prices.

Purchasing clothes in real life work the same way.
There are no set prices for nike flyknit, or converse all-stars.
It all depends on where you buy it from, and what the shop chooses to price it at.

Sure there is an estimation. But it all goes down to whether you are willing to pay for it, and whether it is on sale.
Not everyone loves Nike shoes. Some prefer Puma or Adidas. That's life.
And that's the reason why i'll pay more for hats i like and less for hat's i dont :)

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List of Previous/ Currently owned Cool Stuff
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#1 Sormy Storm Bolted Birdcage (~12k)
#2 Dead Presidents Hoodie (~14k)
#3 Terrorwatt Conquistador (~19k)
#4 Searing Plasma Hottie's Hoodie (~28k)
#5 Power Surge Conquistador (~25k)
#6 Dead Presidents Peacnik's Ponytail (~35k)
#7 Morning Glory Plug-in Prospector (~30k)
#8 Blizzardry Storm Slope (~35k)
#9 Vivid Plasma Hoodie (~30k)
#10 Atomic Head Full of Hot Air (~30k)
#11 It's a Puzzle to Me Sombrero (~40k)
#12 Vivid Plasma Dixie (~16k)
#13 Poisoned Shadows Hoodie (~67k)
#14 "Cool" Forest Fire Flame thrower (~24k)
#15 Blizzadry Storm Barnstormer (~19k)
#16 Green Energy Jumper's Jeepcap (~40k)
#17 Death @ Dusk Hoodie (~53k)
#18 Australium Rocket Launcher (~55k)
#19 Circling Peace Sign Mongolian (~10k)
#20 Craft #46 Deep Cover Operator
#21 Orbiting fire Brainiac Headpiece (~30k)
#22 Spec ksAustralium Minigun (~20k)
#23 Sunbeams Respectless Glove (~36k)
#24 Morning Glory Cadaver's Cranium (~21k)
#25 Australium Knife (~25k)
#26 "Isotope" SMG (~13k)
#27 "Energy Orb" SMG
#28 Time Warp Jeepcap
#29 Stare from Beyond Harmburg (~55k)
#30 "Cool" Brain Candy Minigun (~40k)
#31 Strange Smoking Big Chief (~11k)
#32 Cloud 9 Helmet without a Home (~16k)
#33 Searing Plasma Rimmed Raincatcher (~28k)
#34 Orbiting Planets Noir (~12k)
#35 Green Confetti Lucky Shot (~28k)
#36 Killawatt Cyborg Stunt Helmet (~12k)
#37 Spec Ks Australium Force of Nature (~16k)
#38 It's a Mystery to Everyone Sombero (~33k)
#39 Australium Wrench (~26k)
#40 Vivid Plasma Full Meta Drill Hat (~32k)
#41 Circling Tf2 logo Berliner's Bucket Helm (~21k)
#42 Anti-Freeze Hoodie (~80k)
#43 DbdSteel Shako (~22k)
#44 Vivid Plamsa Towering Titanium Pillar of Hats (~33k)
#45 Blizzadry Storm Pencil Pusher (~38k)
#46 Searing Plasma Engi Cap (~20k)
#47 Disco Beat Down Bonk Leadwear (~17k)
#48 Australium Scattergun (~38k)
#49 Green Energy Larrkin (~40k)
#50 Festive "Cool" Braind Candy Minigun (FT) (~40k)
#51 DiscoBeat Down Buckaroo's Hat (~18k)
#52 Haunted Ghosts Pom Pom Provaceur (unpriced)
#53 Death @ Dusk Firewall Helmet (unpriced)
#54 Cloud 9 Bonk Leadwear (~27k)
#55 "Cool" Turbine Torcher well-worn (~25k)
#56 Frostbite Jumper's Jeepcap