If you're able to find popcorn "seeds" (I've always called them kernels...?), you can just put some into a brown paper bag, roll the top of the bag down a few folds and secure it firmly while leaving plenty of room for the bag to expand, then microwave on high 'til the popping slows. Then take it out of the microwave, give the bag a little shake, carefully open the top and add your own salt, butter, or whatever you want.
This doesn't give you the tongue-destroying bag of death to lick in the end*, but it does give you cheap servings of microwave popcorn. And no additives or dubious substances, if you're concerned with thst sort of thing. Plus, paper is widely recycled.
*We all lick the microwave popcorn bag, right? That's not just me..?