What I Used:
-Coconut Palm Liner ($3.00 @ Wal-Mart)
-Twisty Ties (the annoying ones that make it impossible to get your child's toy out of the box)
-Permanent Magic Marker
Total Cost: $3.50 including flowers.
I went with the flowers I did because they only need partial sun and my door doesn't see much sunlight. If you get full sun you could put some really beautiful flowers in.