You can pay for just one month at a time. I pay now and then and check in on my personal domain – like you, I use dozens of email addresses with a catchall.
I wish HIBP had a solution for those of us who are individuals but use domain catchall forwarding as our method for separating accounts.
It feels good to see adobe@mydomain.com, newrelic@mydomain.com, internetarchive@mydomain.com, etc. there but not any of the addresses I use for normal communication.
I wish there was a "I'm just one person, or a small family" tier for this.