If you enabled Google Billing for a project you still can use the max allowed FREE Api-Calls.
I did never come over the quota in all the years i am using Google and never had to pay anything.
And i am using a lot of apicalls using GoogleCalendar Api and some (10-50) Directionapi-calls a day.
You still have to pay, right.
For example i use 3000 directioncalls i have to pay $30 for them. But i get $200 for Apicalls for free every month.
Even with my 3000 directioncalls i am still in the limit not to pay.
Paying is needed if you used more than you get for $200 for Apicalls.
I might need 100 queries a month
100 Queries a month for which Apicall?