>>38903
no. You can do a chan/text-BBS in pure PHP with no asynchronous server calls, client side scripting, or anything else of that nature. See all of the chans on Tor, where they're paranoid about client side scripts.
The server CPU load would be slightly higher than with a pure static HTML service, but the bandwidth difference would be negligible.
You've gotta consider what's actually going "down the tubes" with each request to the server.
Static page: basically text + formatting that was written by a human hand.
PHP page: text + formatting that's been generated by a program on the server.
AJAX: page is constantly retrieving new data from the site asynchronously. Think: social media pages that have constantly updating feed/status bars set in iframes on the page.
The biggest things that, IMO, will bulk out a page in terms of bandwidth-to-data (aside from asynchronous/automatic data retrieval) are
>images
>large CSS files.
>external JavaScript/client side scripts
Message boards don't need any of this, as all of their work is basically presenting the current status of an SQL table in a readable format, where all formatting is done server side.
View this page's source. Minus the CSS, Client side scripting and images, that's all that is really needed to present an imageboard…a good 45k document. Not really that much per request, especially on a true local meshnet where everyone is operating at the maximum theoretical speed of wifi.