If you have AppleCare+ then the incident would be labeled as "other damage" and will cost $99 to be repaired. If it is not under warranty, then it will cost $349 to repair the phone. You can check your warranty status at checkcoverage.apple.com Although this pricing is subject to change and the best answer you can get is a quote at the Apple store.
The best thing to do would be to take it to the Apple Store and ask the tech Wizards there what the estimated cost would be. That way you would have a fairly definite idea of what the cost would be.
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