We use a popcorn bucket from Tokyo Disneyland and make our own, it's saved us a fortune, particularly as my child prefers the ones we make at home to the store bought kind.

A favourite savoury topping is to lightly spritz the popped corn with olive oil and add a little sea salt and flaked nori seaweed. You can also add some lightly crushed toasted sesame seeds. If you are feeling indulgent then the vaguest dribble of runny honey melds well with these flavours but it isn't necessary.
Nori seaweed is virtually calorie free, and very tasty.

Have you tried mixing a little soya sauce into your butter? Works for us - and black pepper is another option.