Washington state has had vote-by-mail for everyone for a while now too. This year they made it free to mail back the return envelope, which made a good experience even better.

IMO it should be called voter suppression when this isn't done (as in Oregon) since rural voters are less likely to have convenient drop boxes. Mild voter suppression compared to what some states are doing but still politically motivated voter suppression.

Rural voters are likely not strangers to buying a $0.40 (or whatever they cost now) stamp and putting things in the mail, since they almost certainly have to mail other things in (e.g. bills).

No, you buy the stamp to mail it in, or you can drop it off at various collection sites (e.g. library).

For California at least, it's free within the US. Though I had to put a stamp on to vote from abroad.