USPS Flat Rate boxes?
The one I had was like $8.50, but there is another size or two. All you do is go to the poast office, tell them you want a couple of flat rate boxes, and they’ll give them to you. You dont have to pay for them until you fill them up and send them. It doesnt matter how much they weigh, so you can put as much as you can fit in. They’re pretty cool because the one I got didn’t even need tape.