You can buy the corn by the kilo instead of buying small bags of microwave popcorn every time. It’s way cheaper after a few batches, and you can add whatever you want. It’s also neat because you don’t need any oil or butter, I just add a little bit of water, sugar or salt. You can even first caramelize the sugar a bit with the water (in the bowl), before adding the corn.

I think I got such a bowl for below 10€

Costco microwave popcorn is about 36 cents a bag