League is a free to play game, but unlike most models these days its not pay to win. But it still has long, long grinding times to get all the unlocks of different champions. There are also purchasable character "skins" which change the look of your champion during games, of which I have 18.
So basically the cost is saving the buyer from many many hours of grinding for the runes (think glyphs in wow but there are 30 slots per character) and champions, and also a bunch of skins that have already been payed for. 1 of which I know is no longer available, the others I haven't really checked to see.
the cost is between 200 (bid) and 400 (buyout) it depends what this time is worth to someone considering buying an account for the game.
PS. will also accept litecoins