They only charged for battery replacement. I went in for both keyboard and battery issues and the service rep got me a battery replacement to resolve both.Out of AppleCare this is not going to be cheap if they still do it.
I think it depends on where the repair is done. If it's done in-store, the entire top case is replaced. If it's sent away to a repair centre, they will replace only the battery.That’s what they did in the past, but as of this year, they are able to do standalone service.