How much does an iPhone battery change cost?

This is a user-to-user forum. You'll need to contact Apple or an authorized service provider about battery service. You may want to take a look at the following pages:

Batteries - Service and Recycling - Apple

iPhone Repair & Service - Apple Support

$69 to $89 depending on which iPhone model you have.

iPhone Battery Replacement.

iPhone Battery Repair & Replacement - Apple Support