Plastic? Just use a Hole Saw like the ones plumbers and electricians use to cut holes in junction boxes etc.
Here's an example:

https://www.amazon.com/LENOX-Tools-Bi-Metal-Arbored-Technology/dp/B0052EC44Y

Lenox and Milwaukee are the best brands, but, if you don't need it for "production" levels, other outfits sell far cheaper ones, like Harbor Freight.