I wish I could play around with Spanner for personal/side projects, but a production ready instance starts at $65/mo. DynamoDB can run for ~$0.00/month with per-request pricing.
You can! Spanner has a free trial: https://cloud.google.com/spanner/docs/free-trial-instance. Keep in mind, that per-request pricing isn't free unless you stay under the free tier. So just take a look at what those limits are because going above them means you're not free anymore.
This is the main reason I like DynamoDB. I can run side projects indefinitely for basically $0/month.
Same as with lambda. I have a side project that costs $0.42/mo to run.
if you are interested in spanner, you might take a look at cockroachdb. esp the production ready serverless offering which is pay for consumption only. crdb architecture is essentially spanner under the bonnet, GIFFE