You can send it via Media Mail. It's the cheapest way ad it qualifies. It's a couple of dollars. I do recommend putting it in a bubble envelope for safety, but send Media Mail. I've been doing it that way for 15 yrs. Nice auction!
Media Mail is used by the US Postal Service to Ship Printed materials such as books of all kinds, Music CDs, DVDs, Scrapbooking papers, notebooks... It takes a bit longer as it's the slowest delivery but it's also the cheapest, if the item that you are shipping qualifies. Hope that helps! :D