And then come the WP plugin license fees, which easily quadrupel that cost, if not more. Just the other day I have seen a WP instance, that has >50 plugins installed, some of which cost 800 Euro per year. They are lock-in traps for hapless marketing and other non-technical people, who are convinced that they definitely need this super-duper plugin.
And then come the legal fees for making the site actually conforming with the law, such as GDPR. Those fees are increased, because of people wanting to do stuff they need to declare to visitors of the site, for which they want reassurance, that all is well.
And then come the costs for paying a dev anyway, to fix things that they break or that become broken over time.
So no, 9.99$/month are very very far from a realistic price these businesses pay.
And then come the legal fees for making the site actually conforming with the law, such as GDPR. Those fees are increased, because of people wanting to do stuff they need to declare to visitors of the site, for which they want reassurance, that all is well.
And then come the costs for paying a dev anyway, to fix things that they break or that become broken over time.
So no, 9.99$/month are very very far from a realistic price these businesses pay.