cost isn't part of MCP in the same way that cost isn't part of HTTP. It wouldn't really make sense to include that in the protocol, just put it in the application layer on top.
It's a little different. These are systems which are explicitly able to achieve better or worse outcomes by tuning the cost, in ways that aren't especially configurable otherwise. For an HTTP API, you can read the docs and use the small image vs large image endpoint or whatever and have a clear idea of what you're getting and for what cost. For LLMs, it would be very nice to be able to communicate about the desired and actual cost breakdowns for each sub-action.
It would also be nice to do that for http for the same reason. You can also read the find Docs for your MCP, and the LLM can also read the docs
Especially since the cost in some (most?) cases won’t be from the MCP server but from the LLM using it