The domain search feature on haveibeenpwned is/was free. I registered my domain on haveibeenpwned back in 2017 and I got two emails about breaches, one in 2020 and another in 2022. I did not pay.
Log into dashboard, under business there is a domains tab. Enter your domain there and verify ownership. Didn’t ask for payment.
Edit: When I try to do a domain search I get told:
> Domain search restricted: You don't have an active subscription so you're limited to searching domains with up to 10 breached addresses (excluding addresses in spam lists).
My domain has 11 breached addresses.
But I think you are right, because I only have 3 breached addresses under my domain (I do see the 10 addresses wording under subscriptions)
I understand, but it's frustrating.