Battery

Unfortunately there is no set price in Oman. Also - there's the possibility that an Apple authorized repair shop may not actually replace the battery, but might just replace the entire device for a battery replacement equivalent price.

https://support.apple.com/en-om/iphone/repair/service

Battery replacement

You can get your iPhone battery replaced at an Apple Authorized Service Provider. Our authorized locations use genuine Apple parts.

The Apple Limited Warranty covers a battery that fails from a defect in manufacturing, but it doesn't cover batteries that wear out from normal use. The cost to replace a battery depends on your iPhone model and if the issue is covered by warranty or consumer law.

I can't find any price in Oman other than for aftermarket batteries being sold.