Quick question: How does 2 day Prime shipping not kill FBM?

I have a small, physical item (spiral bound book) that ships in padded envelopes (4 inches x 9 inches).

It weighs about 6 ounces, and qualifies for USPS Media Mail – so, typically around $4.25 to get mailed. However, 2-day shipping can easily be $30 for the same item.

If I were to go FBM Prime, wouldn’t that 2-day shipping at $30 kill my margin?