Which cloud model is the most expensive?

Can you clarify for me which cloud model is generally considered the most expensive in terms of cost? I understand that there are various cloud computing models available, including Infrastructure as a Service (IaaS), Platform as a Service (PaaS), and Software as a Service (SaaS). Each of these models offers different levels of abstraction and management responsibilities, but I'm interested in understanding which one tends to carry the highest price tag. Is there a particular reason why one model might be more expensive than the others, or does it depend on specific use cases and requirements?