Wrap them in some bubble wrap & you can send in the small Priority Flat Rate Box for $4.75 if you print the shipping label on USPS.com website. If you don't have the box, you can go to the post office, but they will then charge you $4.95.
If you print the shipping label on the USPS.com website, you get "free" Delivery Confirmation. It's extra if you mail from the post office.