Simple coasters designed right within PrusaSlicer.  Drop in any shape and size it to whatever you'd like.  Standard coaster sizes (according to the internet) is anywhere where from 89mm or 3.5" to 102mm or 4".

I designed my coasters with a 0.2mm layer height, 4 walls, 4 top & bottom layers and the infill of your choice set at 10% density.  With a color change at 1mm and 2.4mm.  This gives you a 3mm coaster with lots of room to show off the infill.  I also made one at 6mm for a thicker coaster as well.  Please note I increased the width of the infill file from the standard 0.45mm to 0.48mm to give a beefier infill line.  Also make sure to check the seems to aligned or rear so they all line up nicely.  I put a snapshot of all on my settings with the photos.

The beauty of this coaster is its super simple to configure if you want to change the size.  You can play with the speeds as well to print them quickly.

On my Prusa Mini the 3mm coaster take about 45min and uses about 15g of filament total and the 6mm coasters take about 1hrs and uses about 20g of filament total.

Enjoy