Upon setting up your billing account, you will be entitled to have one time $300 free credit (Usable for any Google Cloud Platform products) and a monthly recurring $200 free credit (Exclusive for Google Maps API only), the Geocoding API is currently priced at 0.005 USD, with that said, you may have the following requests as follows:
300 USD / 0.005 USD = 60,000 requests
200 USD / 0.005 = 40,000 requests
If you haven't used your one time $300 free credit, then you may have 100,000 geocoding requests for the first month, then for the succeeding months, you may have 40,000 geocoding requests that will be covered by the monthly recurring $200 free credit.
You may learn more about the pricing by visiting the pricing sheet
You may also use the Pricing Calculator if you'd wish to compute for other SKUs as well, note that this also take your free credit(monthly recurring $200 only) into account.