https://www.usps.com/ship/priority-mail.htm
You will need shipping tape, paper or bubble wrap and the post office has a medium or large size box (no cost for the box)
The delivery time is 3 days and the shipping rate is fixed based on the size of the box. The cost is $15 to $20. I have shipped around five times with no problems. The post office will ask about the contents and I tell them it is tomatoes and they are fine with that.