Through folding: ounces flat in a 9x12 is $1.98; folded in a #10 it's $1.11. Square envelopes pay $0.49 extra.
Print package labels online: a 12 oz package coast to coast is $13.65 at the counter, $8.95 through USPS's free Click-N-Ship.
Keep boxes at or under 12x12x12. Since July, anything bigger is billed at volume ÷ 139 pounds if that exceeds its weight.
I've been building an (unofficial) searchable reference to USPS's rules and prices. The presort page is here: https://postalref.com/guides/presort
What was the reason for the 2026 change to make it non-free? Some "government should be run like a business" (and therefore charge for services) BS, or was there some kind of abuse or privacy issues they were trying to limit?
All governments provide some services for "free" and charge for others. Sometimes it makes sense, other times it really is BS.
They spun it as supporting the new RestAPI based system they put in place, it does have more efficient rate limiting, and some controls like Mailer ID verification (able to tie who makes a request for a label to that actual label, etc.) that are supposed to help with fraud.