Cheapest way to ship a textbook expedited mail sold through Amazon?

I need to ship a textbook I sold through Amazon. They gave me $6.99 to ship it and it must be shipped expedited (within 3 business days). What are my best options? I can't do media mail since it is expedited. Thanks for your help.Cheapest way to ship a textbook expedited mail sold through Amazon?
Go to the post office and ask them what they recommend. I'm sure they know what's best.

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