Do you mean cost of the overhead for the client or the cost for the server? One way that it is advantageous for clients if they can afford it is that it stops

Do you mean cost of the overhead for the client or the cost for the server? One way that it is advantageous for clients if they can afford it is that it stops e.g. isps from inserting ads into webpages, which is good. If a client can't afford to use the https, they can opt out I would think?