Lets see, my Wordpress install running a well known theme, using Wordfence to alert for plugin updates, with me keeping an eye on it cost about £2,000 to set up and has ongoing costs of about £1,000 a year.

No. Its not cheaper to hire someone to hand-code the site and then hand-code every change.

If you're doing that, just use wordpress.com. Wordpress is way out of scope for the term "enterprise CMS".

So we've gone from "there's no need for a CMS, write HTML flat files" to "Use a hosted CMS" - OK.