How much would it cost to get a smashed up iPhone 4's screen fixed?

I smashed up my screen my iPhone 4 quite badly. Everything works perfectly fine, my notifications still work, all my data is fine, it charges up, my speakers everything. Even though i'm getting a new phone in November, i still want a phone in good condition.

If your contract is up, then I would just trade it in and get a new 4S free (plus some credit for your broken one). Or use that to upgrade to a newer version which would make it cheap to upgrade.
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Apple also recently boosted the trade-in values for the iPhone 4 and the iPhone 4S. Apple Stores now offer up to $99 toward a new device for an iPhone 4 and up to $199 for an iPhone 4S.

It should be about $80-$100