Costs are all over the place because some dealers will try to upsell you on non-required or completely unnecessary maintenance (like injector cleaning) - refer to your warranty and maintenance booklet for what's actually required, then decide if there are any extra things you'd like done (e.g., most choose to do change diff fluids, but not plugs).
Now, that said, please spare us yet another one of these threads and just copy/paste this into google. It will give you most of the 60k service discussion for Gen 5s. Happy researching:
60k cost site:subaruoutback.org/forums/138-gen-5-2015-2019/