Scratch

For the iPhone Service Answer Center click here --> Choose Your Country or Region - Apple Support

Select your country.

For a cost estimate:

- Scroll down to "Get an estimate"

- Enter the service required

- Enter the iPhone model you have

- Enter the version of that model

- Click "Get estimate"

For instructions on how to get your iPhone, iPad, or iPod touch ready for service click here --> Prepare your iPhone or iPad for service - Apple Support

- "To protect your information and save time, follow these steps before you get service for your device."

As for warranty cost, it isn't covered by that or might not even be considered by Apple to be worth worrying about:

http://www.apple.com/legal/warranty/products/iphone-english.html

WHAT IS NOT COVERED BY THIS WARRANTY?

"This Warranty does not apply: (a) to consumable parts, such as batteries or protective coatings that are designed to diminish over time, unless failure has occurred due to a defect in materials or workmanship; (b) to cosmetic damage, including but not limited to scratches, dents and broken plastic on ports;

Without an AppleCare+ plan, then assuming Apple would charge the same as they would for a cracked screen, their estimator says that it would cost $349 US plus any applicable taxes.

iPhone Repair & Service - Apple Support

Prices in other countries will differ.

Regards.