A4C offers the Bike4 Bicycle Mount for iPhone 4/4S in White for $9.95 with free shipping. That's tied with our January mention and the lowest total price we could find by $3. This waterproof case attaches to your bike's handle bar and features a fish-eye lens and openings for the headphone jack and camera.
There's a less expensive way, and then there's the way that works for you. The two may not be the same.