How much does the time machine cost for 1tb

Time Machine is built-in and free to use. You need to provide a suitable external disk and a good one can be had for around $100 or less. Keep in mind that for TM a disk of about 3X the amount of data you are backing up will be needed, as it will grow over time. The disk needs to be formatted Mac OS Extended (Journaled).

Back up your Mac with Time Machine - Apple Support

Any USB3 or USB-C connect external HDD can use for Time Machine drive something like followings.

https://www.amazon.com/Seagate-Portable-External-Hard-Drive/dp/B07CRG7BBH/ref=sr_1_4?crid=3A4XLU96SBFC3&keywords=external+hard+drive&qid=1566565246&s=computers-intl-ship&sprefix=external+%2Caps%2C289&sr=1-4

https://eshop.macsales.com/item/OWC/ME3UH7T1.0/

You need to purchase USB-C to USB3 adapter, also.