[instarx]

Go to the Home Depot and by one length of vinyl gutter (the good architectural kind, not the cheaper "U" kind, it's still only about $4). Cut it lengthwise so you are left with an "L" shape. The back part of the gutter becomes the air dam and an inch or so of the bottom of the gutter becomes the forward-facing "L" mounting tab. Use the short L-tab part to attach it to the car with screws, velcro, or rivets. If you make a few straight cuts in the L part in strategic places the airdam part will curve nicely where it needs to (see my pics). The air dam is about two inches deep - just about the perfect height for my car. Any lower and it would be a pain at curbs and entrance dips.

I did this with my Volvo, attached it with industrial velcro and double-sided tape, and it looks great - almost factory. It can be painted if you use a vinyl paint.