For battery replacement you really want to take this to a local electronics repair shop (read the reviews so you find a good one). They'll do it same day or next day.
It'll probably be around $200-$300 if you want an official battery. More like half that if you're willing to accept a 3rd party one.
Apple doesn't sell the official battery as a standalone part even to Authorized Apple repair shops, so anyone telling you they're installing an official battery is already lying to you or putting in something used.
Even if a local shop somehow sourced a legit, new Apple battery, why wouldn't I go to the Apple Store if it's the same cost and would only be the battery?
(For $299, Apple replaces the speakers, touchpad, batteries, top case, and keyboard and provides a parts and labor warranty for 90 days)
It'll probably be around $200-$300 if you want an official battery. More like half that if you're willing to accept a 3rd party one.