: Typically ranges from $20 to $70 on Mercari or eBay.
: Specialized retailers like iFixit and OWC (MacSales) offer DIY kits for internal upgrades, including batteries (approx. $80–$135 ) and SSDs. buy osx
: Recent versions like macOS Tahoe are free downloads via the Software Update section in System Settings. : Typically ranges from $20 to $70 on Mercari or eBay