Thanks for the tip @mommdc. I checked and you can order a set of 10 of the boxes for free from USPS online, so I ordered them now since I’m sure we’ll need to start shipping items soon (including a swim suit that got left behind at a relatives’ house at the end of the summer :)). Here’s the link to order some:
However, I also read that “Regional Rate Box prices are available to Priority Mail Commercial Base and Commercial Plus customers who use one of the USPS-produced Priority Mail Regional Rate Boxes” so I’m not sure if I can use them as an individual? Is there still a way to take advantage of the lower rates?