I had a scratch on my "Blueberry" Dodge Caliber. Someone hit my car in a parking lot a few months back. Here's the scratch before attempting the repair.... Just above the passenger side rear wheel.
I went to the local Walmart and spent $1.97 + tax for Sally Hansen Hard As Nails Nail Polish 730 Frozen Glacier
I had a four-sided nail buffing block already onhand.
After sanding the rust off and blowing off the loosened rust, I painted on the paint. Not too bad...