The starting version of Datomic Pro is more likely to be more affordable than the free version because it supports all storage services as a licensed version of pro. As for local storage and bandwidth, I would say that it can store up to the amount of free disk space. The transactor processes all the records, so I would suggest that your only potential bandwidth bottlenecks are the hard drive, or if you throw tons of transactions at it, it will wait for the indexing work to complete as your data grows. Indexing can become expensive in terms of costs over time, and it is best to have GC and excision work if you do this large amount.