Edit: just got a quote for an iphone 7+ battery replacement from one of the mall kiosks here: $120. If there is so much fat in the cost surely they'd at least undercut Apple by $20 to get the business.
Removable batteries are a completely different conversation but you can still buy phones with them so go ahead and indulge yourself.
Undoubtedly genuine Apple batteries may be better quality but that's still ~$100 for labour.
You're not only paying for the labour, but also a guarantee the phone will work as intended after and warranty on the replacement. $100 is cheap for that.
Because it is designed to prevent user from replacing battery, so you pay $100 for opening the lid, taking out the battery, putting in the new one, and closing the lid. $100 is nowhere near cheap for something that should be safe to do for the user.
$100 _is_ cheap for the phone as it currently stands.
Only if you're Apple's fanboy. Virtually anybody else still has replaceable battery.
"Apple is reducing the price of an out-of-warranty iPhone battery replacement by $50 — from $79 to $29 — for anyone with an iPhone 6 or later whose battery needs to be replaced, starting in late January and available worldwide through December 2018. Details will be provided soon on apple.com."
It's the end of Moore's law and they are going to start pulling this stuff so you upgrade, because the new phones just aren't that much better. Meanwhile, I'll stick to Note 4s still they stop making them and I can't get them used. Perfect phone, imho.
Off-brand batteries can be dodgy and not have the correct protection circuitry.