One of the most characteristic elements of all RuneScape and RuneScape Old School is the Grand Exchange, a marketplace where all players can freely sell or trade their items.
Prices within the Grand Exchange are defined entirely by players, based on supply and demand for the items for sale.
Due to the fluctuating market of the Grand Exchange, many players use various strategies to determine whether an item will increase or decrease in price and thus make a profit by buying and reselling at the right time.
The Blue Partyhat has a very small importance within the RuneScape plot, specifically in the Wise Old Man story.
But, this item was discontinued completely, while the number of RuneScape players only continued to grow, so the Blue Partyhat became quite scarce and therefore its price began to rise disproportionately.