League of Legends is an entirely free game and doesn’t need any money if someone wants to play it. However, almost every league player has purchased at least one item out of the Shop, be that skin, a chroma, a hextech chest, or something else. Every transaction in League completes through Riot Games’ currency which is usually known as Riot Points or RP. If a player spends “real life” money in League, he is buying RP first. Then, he uses RP for buying some favorite skins as well as emotes.
https://www.sportda.com/how-much-money-have-i-spent-on-a-league/

Different champions possess differently-priced skins which have their exceptional value. In simple words, a player can get his favorite thing in League for $5 or $50. The amount will depend on what that thing is. Many champions comprise game-changing skins that most of the League community ends up buying.

How Much Money I Have Spent in League
It is not an uncommon reality for a League player to get carried away and spend too much on the game. Some simple steps help you to determine how much money you’ve spent in League. There will be a red option saying “Show me the money”. Just click the button in the middle of the text. After the completion of the 3rd step, all the money a player has spent on that specific account and in that particular area will be displayed instantaneously. If a player has ever transferred the League account to one or multiple servers, then all the spending on those servers will not be shown here. After the transfer back to those regions, the money will be available to check.