In the U.S, $149 if not covered by AppleCare+. See:iPhone Screen Repair & Replacement - Official Apple Support
Repair prices are listed on Apple's web site - iPhone Screen Repair & Replacement - Official Apple Support
(change the country as necessary with the small round flag icon in the lower right).
Note that the display glass by itself cannot be replaced - the repair price is for an entire replacement display as the display is manufactured as a single integrated unit, sealed together at the factory.
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