you can probably get a sense of it based on your own usage of terraform and the log output (or the time various resources take to get managed in the Terraform Cloud/Enterprise UI). I think in the majority of cases you'll see that the bulk of the compute time is actually network bound, not because of the number of resources, just because the server at the other end (AWS, Azure, GCP, etc.) is doing a lot of work. I know in some cases things like SQL Server Clusters on Azure can take literally hours to provision. Terraform will spend that "compute" time sitting there waiting, it's not actually doing much resource intensive though.
And then at the end as you said "stores the new state". Which is basically a big JSON file. 10 resources? 1M resources? I'll leave you to work out how much it probably costs to save a JSON file of that size somewhere like S3 ;)
And then at the end as you said "stores the new state". Which is basically a big JSON file. 10 resources? 1M resources? I'll leave you to work out how much it probably costs to save a JSON file of that size somewhere like S3 ;)