I recently discovered a store called Five Below, everything there ranges from $1 to $5. They have a pretty nice selection of nail polish at 3 for $5, and a few other types at 2 for $5. I actually got several of the 3 for $5 ones at the recommendation of a friend. I painted my toe nails with the Mermaid Lagoon color, which is a mixture of different sizes of blue, purple, and pink glitter, and in just 3 days I've gotten more compliments on it than any other pedicure I've ever had, professional or not. It's a deal that's definitely worth looking into if you paint your nails regularly!
I bought nail art polishes, which are the ones with the really skinny brushes, from Five Below and I really liked them. I have yet to buy any others from them yet. Five Below also sells Nicole by OPI nail polish for $4, which is about 50% off normal price. For anyone who isn't familiar, Nicole by OPI is salon-quality nail polish. T.J. Maxx also sells two-packs of Nicole by Opi for $8. They also sell Essie for $4, which is another salon brand that is usually about 7 or 8 dollars. I'm a huge nail junkie and I squeal with delight when I can snag a salon polish for relatively cheap.