$4000 USD a year he better be delivering caviar to your doorstep (that shit is cheap now)
It's because of Enterprise contracts, for the things you can check off with HIBP... 4 grand is not a lot for them. But, then also if you offer a separate plan and just say 'no enterprise, we trust you', many businesses will just ignore the enterprise plan.
I am not sure what you are talking about.
I have a domain registered and can see exactly which addresses have been compromised by what, without payment.
I see this:

Interesting.
I see a list of email addresses.
~~Perhaps that message only shows up if some of the results are from the paid lists. For me, I don't see anything listed beneath, even though 34 addresses match, so I guess nothing's in the free lists.~~
edit: Looks like it's triggered on number of results:
Most domain searches are free. Once a domain has more than 10 breached email addresses on it, searching the domain requires a subscription. There are several ways to either reduce or entirely remove the need to have a subscription:
That's interesting, since my list of addresses contains numerous ones that don't exist and nobody here has ever used.
Maybe not an exact fit for your situation and would take work but I use addy.io. solid and have had no issues with it for 4+ years.
If it takes me on average 5 minutes to login and change an email address, it would take me about 1 days, 18 hours to change them all! It definitely looks worth it for others who want to start using aliases.
Just register a new domain and route that mail to your old domain.
Self-hosting
Hosting your own services. Preferably at home and on low-power or shared hardware.
Also check out: