I'm not sure the log message v structured message comparison makes sense - most log and trace events are batched and compressed before being transported, and so the size difference isn't really an issue. On the receiving side most services have some kind of column store as their main datastore and so there's no issue there either. The benefits of structured logging are worth it.
Regarding pricing - there is an option for every kind of usage out there, it's mostly a solved problem that comes with choosing two of large scale, low cost, low latency. For instance we serve large scale and low cost.
(co-founder here) Try axiom.co - we support splunk-like query syntax, dashboards, monitors, unlimited sources/hosts/etc, and you get 500GB/mo ingest + 30 days retention on the free plan.
Regarding pricing - there is an option for every kind of usage out there, it's mostly a solved problem that comes with choosing two of large scale, low cost, low latency. For instance we serve large scale and low cost.