Do you expect to find a company that sells a calendar-only subscription? "Calendar - 49c/month"?
I've been looking at lot at all kinds of services and most start their pricing at around 5 USD/month. Regardless of how much actual features they actually provide.
I'd say your best bet is NextCloud. You can rent some, self host or use a free instance (there's a couple around).
Personally, I'm self-hosting stuff on a VPS. For whopping 5USD/month I'm getting things I'd be paying 50, if not mere, if they were offered as separate products by your average service-providing companies.