Whether or not the price is right is another discussion, but I will point out that they’re not charging for you to see the events. Like you said, there’s a web server and API for that. They’re charging you for them to store the history and serve it up on demand, which does have ongoing costs and I understand not accepting a one-time purchase for.

If you want history, hook into the API with Home Assistant or Grafana or something and store it yourself. It’s either that or pay them to store it. Infrastructure that stores and serves up the history doesn’t come from nowhere, and an ongoing cost for an ongoing service kinda makes sense.