Do i have to pay 69.99 for microsoft excel for my mac computer

I'd recommend getting Office 365. Microsoft does not give away their software so yes, you must pay for it. If you need Excel you need to either subscribe to Office 365 or purchase a license of the latest version of Office for Mac.

Other options are to use a clone such as LibreOffice which is web based and free. You can also use the Numbers app that is likely already installed on your system.

Of course you don't have to. Use FreeOffice, LibreOffice or the included Apple spreadsheet app.

an alternative could be the free libreoffice suit it works with excel files

think apples numbers app do too

Sometimes your company will let you purchase it at a discount.

Yes.