I have to agree with jamesqf, wait until the 2012 elections are done. Bring your dykes with you and fill your trailer with the stuff. Most gas stations and convenience stores use coroplast to make their signs, wait till they close.....
Can't wait, look up plastic sales in your area. They usually have pallets of of it in 4x8'. I have gotten some at sign stores but they think you are trying to muscle in on their sales of signs and charge an arm and a leg.
Good luck
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"A man is not finished when he is defeated. He is finished when he quits."
Richard M. Nixon
"The reward of suffering is experience."
Harry S. Truman