They get progressively cheaper as we approach February 28. After that, I believe registrations are free with a $12 maintenance cost.
Minor correction, registrations are never free. Come 2019-02-28 16:00:00Z, they will be available at the base price. Registrars set their own prices, so depending on which registrar you're using, expect that to be around $12-20/yr (including the initial year).
Do you happen to have a source for the 16:00 UTC base price switch? I am not seeing a specific time on any of the linked pages.
Free in the sense that there is no initial up-front cost (compared to the pre-sale pricing). Everything else is an initial dollar amount ($11,500, $3,500, $1,150, etc.) in addition to the $12 maintenance cost. After February 28th, there is no up-front cost but there is still a maintenance cost.