The updates to Office 2019 will always be free. They are released monthly and are a combination of bug and security fixes.
And by "updates", they are updates for Office 2019 which will always and only be Office 2019. The same as updates for Office 2011 never changed it from 2011 to any newer version.
MS has hinted 2019 may be the last perpetual license version. It's really only cost efficient for the user who will keep using that version through as many major OS releases it will run under (and MS themselves continue to support). Otherwise, if you price it out, the subscription versions actually cost less when you have even just two people using a 365 plan.
The $99 per year fee for six computers is a far better value than getting individual licenses for Office 2019. When you figure a perpetual license release has been happening roughly every three years, $300 over that time is much, much less expensive. If you were to purchase six Home version editions of Office 2019 (the one without Outlook) at $150 per license, it would be $900. For the Home and Business edition with Outlook, it would be a whopping $1,500! Then you'd spend that again about three years from now if you always get the latest release when they become available. Even installing Office 365 for only two devices is cheaper than the perpetual license Business edition ($500). Plus, since you can install Office 365 on any six devices you want, that means you can also install a copy in Windows so you have a working install of Access, which there has never been a Mac version of.