Yeah, I don't get how it'd be cheaper at all. Yes you need a backend anyway, but unless you're not paying for usage and have spare CPU cycles and bandwidth available, it's not cheaper. It's cheaper to send your frontend html+js and let the browser cache it so it's only sent once, and let the frontend pull only the data it needs to render the html. The backend isn't having to process a template, or resend similar html constantly to the frontend since most of that likely cannot be cached.