I booked mine a week and a half ago thru the website my hotel gave me.
https://www.coronasnelcheck.nl/
It was 29.99E.
A fellow tour member was able to book an appointment at a location near our hotel but I could not get that location to come up on my phone so I just went down to the location near Dam Square on Molsteeg 8. This was a store front with one person doing the testing and results. She was not busy and took me in an hour before my appointment time (I allowed way too much time to get there, lol). I got the results in an hour via email and then did a screen shot and was able to load into the DeltaFly app. I also had to show the screen shot to the Checkin person at Schiphol.
This was very easy.