Hour zero
The registry stops publishing the domain's records. Not gradually. Lookups fail, so the website becomes unreachable and mail delivery stops in the same moment, because both depend on the same records.
Nothing on your systems changes. Your server is still running, your mailboxes still exist, your site is still deployed. Everything is intact and unreachable.
Hour one to twenty-four
The registrar control panel may still show the domain as active, because renewal is technically still possible from their side. This is the single most confusing part of the process and it causes real delay, because the person checking concludes the problem must be elsewhere and starts looking at hosting.
Meanwhile, mail sent to you is bouncing at the sender's end. They see a delivery failure. You see nothing.
Day one to roughly thirty
Most registrars offer a period during which you can renew at the ordinary price. The length varies far more than people expect: generous at some, close to nothing at others, and set by the registrar rather than the registry for gTLDs. The extension matters too, and the assumptions from .com do not carry across.
Throughout this whole period the domain is still not resolving. You are not in a grace period in any comfortable sense. You are offline with an option to recover.
Roughly day thirty to sixty
Redemption. The domain is still recoverable but the fee rises sharply, typically to somewhere between eighty and two hundred pounds or dollars against a renewal of ten or fifteen. The process is slower and often needs a support ticket rather than a button.
The last few days
Pending delete. Nothing can be done. The domain is queued for release and the outcome is already fixed.
Release
This is where the cost curve stops being about money. Expired domains with any history are monitored automatically and registered within moments of becoming available. Age, inbound links and traffic all make a domain more likely to be caught.
At that point you are no longer dealing with a registrar. You are dealing with an owner, if they reply, and the price is whatever they decide. Businesses that have traded at the same address for a decade sometimes find there is no route back at all.
What the shape of this tells you
Every stage costs more than the one before, the domain is unreachable throughout all of them, and the final stage is irreversible. There is no version of this that is cheaper than renewing, which is obvious in the abstract and apparently not obvious in the moment, because it keeps happening to organised businesses.