Huge changes at the USPS this year. It is bigger than inflation for them, they have all kinds of challenges. Inflation is just adding to it.
I recently returned a 1/2 oz. part. I had to put it in a small padded envelope. Their cheapest solution was almost $5. The clerk said it was because of the envelope. The part was $15, so I at least netted $10.
They used to have these envelopes and boxes in the lobby where you could buy them for a few bucks, and whatever you could stuff in them was a "go." That option seems to have been removed.
EDIT: looked it up. "Flat rate priority" still exists. I guess they just removed the boxes from the lobby because of theft? The new "flat rate priority" rates are double of what I remember from about 4 years ago. A small box is now $9. I remember $4. BTW, "priority" means nothing for these. "Priority Express" is their competitive product to Fedex or UPS.
Lots of details here. You may get vertigo reading these:
https://pe.usps.com/resources/PriceChange/October 2022 Price Change - Notice123.pdf