You can go the flat-rate way if you want, but you will pay twice as much as otherwise for shipping. Regardless, you can get priority mailing packaging for free from the PO. They will ship you boxes if you request them off the website.
The vast majority of my cigar shipments are under 1lb, I think most are the same. Just from general recall, I think I needed about 20+ cigars to make it over a pound, including box. I use a
simple food scale from the kitchen to weigh things.