Free, because it's not a product — it's hygiene
Checking a contact or a subscriber never touches your verification credit balance, on any tier — it's a one-click button, not a metered feature. Basic account hygiene like this shouldn't compete with your actual verification usage for budget — you should be able to check every alert contact and every status-page subscriber as often as you want without worrying about eating into credits you'd rather spend elsewhere. It's meant to be run as often as curiosity strikes, not rationed like a scarce resource. It's meant to be used habitually, the same way you'd double-check any other safety-critical setting.