Please use Buy RapidWeaver Classic
With the provided link on this site at Realmac Software Store you can manage your account.
Regarding the business model, see the comment here Foundry3 is not available - #5 by Heroic_Nonsense which is the way I see it as well.
Basically, get the update to RW classic. Then cancel the RW Classic subscription. Move your site to Elements and use the Elements subscription. Cancel that when you are happy with the Elements version you are using, it will continue to work.