The cost of a game depends on the type of game. For example, most mobile games are free and there is no cost to play them. Some full-length PC games can be purchased for $50 or less while others may require a subscription fee and some even offer in-game purchases that allow players to buy additional content such as weapons, health packs, costumes, etc.
For more information about how much money you should spend on this game, contact the developer directly or visit their website for details about the different types of in-game purchases that can be made.