"as little as $65 USD/month" for GCP Spanner vs AWS Free Tier: "25 GB of data storage ... 2.5 million stream read requests ..." https://aws.amazon.com/dynamodb/pricing/ So, there's probably somewhere the lines on the graph cross, but Google's headline seems misleading.
The Free Tier is completely irrelevant here, though. The very reason someone might use Spanner is its excellent scalability. I don't believe there is any reason to use it for smaller projects other than education. The customers who will use Spanners are those for whom CockroachDB is not enough, for example. For everybody with databases that are not that huge PostgreSQL will do just fine.
Edit: actualy Spanner looks like another CockroachDB. You use sql to interact with it. In which case I can see many people who would want to use this with a free tier for hobby projects. ie. in between education and production development.