Cracked screen

The back isn't a replaceable part. The entire phone must be replaced. That's $549 for the X.

https://support.apple.com/iphone/repair/service

~Lyssa

The back is not really all that replaceable. If the back is cracked then Apple's solution is to replace the entire device for the customer. The glass is fused to the rest of the case including the camera cover. Even if everything works, the only fix Apple would give for you is to give a replacement device (could be new or refurbished) for a price less than retail. The replacement would come in a plain box without any accessories. It would also require an exchange of your existing device. The price is the same for a particular model regardless of the storage capacity (i.e. all iPhone X capacities are the same replacement price). The exchanged units goes back to Apple to either recycle or reuse for new replacement devices. If you decide to do the exchange, I suspect that they would probably reuse the logic board in a new case. However, Apple doesn't specifically replace a damaged case for customers.