The PCR tests are about 3000 Baht. That is more than the "per night" price on Agoda. I do not believe these tests are included, even when it is mentioned somewhere on Agoda. It simply isn't possible. Also... I do not believe that you should book now for April. You can be sure that things will change again in the next weeks.
They gave me the same extension some months ago. While airlines have several flights a day to my country. And if you think about it... Why not? Why throw foreigners out if they have money to spend.