It takes an extra twenty cents of stamp, or just double up on regular stamps and you'll be good to go.
When I went to mail our ballots just for fun I went to the counter to make sure we had enough postage. Low and behold a regular stamp for an envelope isn't enough. I guess it's written somewhere on the directions for voting but I missed it. It does say underneath where you put the stamp that if you don't put a stamp on it won't be mailed but it doesn't say how much.
I'm headed back to the post office in a couple of minutes to offer to pay for any ballots without enough postage. Last year they charged the County Clerk. Seeing as it's in the fine print maybe our county (rural, high plains, wheat farmers, kinda conservative like Kansas is kinda flat) won't pay this year.
Update: I added Ohio and Montana to the title from info gleaned from the comments. Every vote needs to count in every state.
Below is the last of our pickings from the garden just because every post needs a photo