US standard is $0 if you have AppleCare+ and $79 if you don’t, across the full range, but only as far back as the S2.

Add an extra $10 if you want the replacement shipped back to, it’s free to collect it at an Apple Store.

You take it in, they check it for other damage besides the battery and if there is none then they accept it for battery service.

You do get a refurb, but this is an Apple refurb so while the internals may have been used before, the case will be completely new and I distinguishable from an off the shelf item.