CSG is unfortunately is a pain to paint buy hand and often is not one of the available color option for prepainted stuff.
I'm in the process of getting my R side skirts painted.
The skirts themselves can get pretty cheap if you do replicas and fit is good at least for mine.
Paint will be the pricey part.
Which ones did you buy? Do you mind linking me? I saw these on ECS but I'm not exactly sure they're the whole skirt or more of a "splitter" kind of deal
https://www.ecstuning.com/b-maxton-design-parts/golf-r-side-skirt-set/vw-go-5-6-r20-s1/