A battery is $70. There are 3 screen prices based on what option you want to do. You can do used, new, or we can replace just the glass on your phone if your lcd is good. Do you know if your lcd is still good?
You can chat on http://www.cellular-freedom.com
Im not sure about a galaxy s8 but my iPhone 7plus cost $90 to replace the screen. If the LED is broken underneath the screen it may be more.
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