Why are Prompts expensive?

Several factors make prompts expensive. First, the cost of the AI models themselves, as explained above. Second, other costs of doing business (such as 30% app store commissions on prompts bought via in-app purchases). Third, although your prompt may be relatively short, there is a lot of extra context that is provided to the model behind the scenes, and although the text in the AI's reply is short, the code may be several thousands of lines long, all of which adds cost and a volume of usage that a free or e.g. $20 monthly plan to a general-purpose AI assistant is likely to block or throttle.