I went to Lowes and spent $60 on supplies for:
Lower air dam
Belly pan
Rear wheel skirts
Upper Grill Block
So... I figure it'll take me a year to recoupe my costs, maybe sooner depending on the difference these will make.
This is a game to me. It's fun and I can't wait to see what kind of improvement I can make. That and I LOVE modifying cars, so this is right up my alley.