that's real helpful
from what i've seen unusuals are spread into 2 parts that determine the cost.
Hat and Effect.
if you have a hat that nobody wants, with a good effect, then it will be worth less than a hat that has a middle effect (say ghosts) and a middle tier hat (duty rag or pyromancer)
Then there's the holy stuff expensive hats like the burning team captain, or a sunbeams team captain
cheapest unusuals are the festivizer with green confetti /purple, tree with confetti, Couple disaster confetti and so on.
if you want a class specific hat such as a demoman it will be worth more even if its confetti.
Most all class hats are low in price with the confetti effect, minus the towering pillars.
those are just as expensive as burning team captains.