Old Navy will have their $1 flip-flop sale this Saturday only. They normally limit the purchases to five per customer. Go here to see the announcement and to find a store near you.
This may or may not apply to outlet locations.
Old Navy flip flops seem to last longer than Dollar Tree and Dollar General $1 options or Walmart's 98 cent versions.
Regular price of the ON version is $2.50. The sale is good for the whole family.