Finally, after a week or so of driving around with the cardboard, I felt it was time to make something more permanent. Research led me to the conclusion that I would have the best luck locating large sheets of coroplast at a sign shop. Sure enough, I found a shop selling them in 4' X 8' sheets for "about $25" as the employee told me. They didn't have any in stock that day, so they said that they would order some and have them in the next day. The next day, I walked in and asked if I could pay with a debit card (since I like to keep the cash in my wallet as change for customers when I deliver pizzas). The man paused and said that I could. Sensing his reluctance, I offered to pay with cash. The only problem was that I only had $22 in my wallet. He then said that was ok, so I already had saved $3 (or almost a gallon of gas) on my new air dam without even installing it.
Then, on another 40F day I installed my coroplast air dam.
Here it is:
I plan to paint it black to match the grill block. Its held in with 6 screws and I had to drill into the plastic covering inside the wheel well to secure it better.