Microsoft offers of Word, Excel, PowerPoint, and OneNote. No installation or activation required.
Avoid eBay "lifetime" keys for $5 (these are often MSDN or volume license keys that get revoked). Instead, use: microsoft office 2016 toolkit and ez-activator free download
Genuine Office 2016 keys (retail) cost ~$40–$70 if you find clearance stock, but beware of grey-market sellers. Microsoft offers of Word, Excel, PowerPoint, and OneNote
Microsoft provides a of Microsoft 365 Family or Business. Microsoft offers of Word