500 square feet. I cheated: we had our municipal election on Monday; on Tuesday morning, I sent email to each mayoral candidate's campaign office asking for signs. (It may have helped that the wording on these made them unusable next time around.)
I'm bumping this thread up because it's coroplast season again!
Now's the time to keep a lookout for good material. Election day is Tuesday Nov. 2nd. As usual, wait until the day after elections before helping cleanup the signs.