Where are you buying batteries that are a significant portion of the price of a phone? For iPhones, authorized battery repairs around usually around $70 which

Where are you buying batteries that are a significant portion of the price of a phone? For iPhones, authorized battery repairs around usually around $70 which is about 6-10% of the price of a new iPhone. Is $70 really so much to pay for a battery that should easily last you 3 years or so?