The recent thread on roller skate keys has me pondering the music of Melanie. Melanie is a Libertarian, so I know she’s cool! 
But when she sings in Peace Will Come (According to Plan),
I don’t know what I’m supposed to do. Please buy one what?
A roller skate key?
I always heard “peace by One”. A search of lyrics archives online shows “please buy one” just as you say. How weird.
I think she’s just a lousy poet. I believe she’s saying “buy” a “chance for peace,” (i.e. take a chance), but (if those lyrics are any indication) she’s a dreadfully amateurish and pretentious poet and chose a bad word.
I’m sure DtC got it- Buy a chance for peace.