Doing battery replace for IPhone 8 ?

AUD $79 from Apple including GST. $19.95 shipping if you choose to ship. An AASP could charge more or less, but expect their prices to be competitive with Apple's.

iPhone Battery Replacement – Official Apple Support (AU)

If would generally recommend going to an Apple Store, but I'm not sure what the situation might be in your area, especially how difficult it would be to get an appointment or even leave the house.

Click on the Get Support link at the top right of this page to start the process. This is a user-to-user technical support site operated by Apple.