The Postal Service has Media Mail, an economical rate, approximately $2.61 for postage for a small bubble wrap envelope (2 for one dollar at the dollar store) to mail a DVD or small book within continental US, no letter or other communication inside. For larger media mail items, say a DVD collection an inch thick, you can buy cardboard case at the dollar store and tape to wrap the ends, mail for approximately $4.61 or 4.81, something like that.
Yeah, Media Mail is quite reasonable. And it even comes with tracking these days. But unless you are mailing Media or lie what you have inside, you would have to spend more at the post office. Their flat rate packages used to be reasonable, but the price keeps going up every time they have a rate increase.
I use Media Mail all the time; it's the cheapest way to go.