Sellers, how much do you spend on packaging materials ?

I'm belgian, buying cardboard boxes at a post office is insanely expensive so I plan on repurposing old ones from things I ordered.

My main issue is, I want to sell items with pretty unique shapes that wouldn't fit in regular packages, mostly rolled posters and Harry Potter wands. I'm pretty sure I'll have to find a cardboard tube for the first one, but I'm not sure how cheap it is. Am I supposed to include the price of the packaging in the price of the listing aswell ?