The initial cost is 18.5 € / 25 $ to set up your page but that being the only cost independently how much music you put up. Then they will take a 30% commision on your sales unless you let it for free. Think that Google could have been a little bit more generous with the commission maybe 15-20 % would have been better for both the artists and for Google if they want to compete with other similar services.
Another hmmm from me would be that it is not for all countries.
For example China, India and central and South America (Mexico yes) is not included...
In either case if you are going to publish your music it can be worth a look?
Plus of course you should go and take a listen to Caustic Replay and if you can support!
Google Play Artist Hub
Caustic Replay album