Amazon has a new sample box available exclusively for Prime members: Buy the Optimum Nutrition Sample Box for $7.99 and you’ll get back a $7.99 credit to spend on full-size products! You can look at this as getting the box for FREE after the credit!
Note that once the box ships they will email you a link to shop the available selection of products. At checkout, the credit will be offered to you as one of your payment options (it used to automatically deduct it, but now it’s in the payment section and you need to manually select it). If you missed the email, simply go to the Amazon Sample Box page to find your boxes; you can then click through them to access the full-size products.