If you want just the local repo, try this:
mvn help:evaluate -Dexpression=settings.localRepository | grep -v '\[INFO\]'
EDIT
I’m revisiting this after years because recent versions of the Maven help plugin introduced a useful parameter for the evaluate goal called forceStdout that allows us to remove the need to grep the output:
mvn help:evaluate -Dexpression=settings.localRepository -q -DforceStdout