Some people felt burned by Vault where it looked like the free version could be used in production but it couldn't and then the enterprise version is very expensive.
Production-worthiness depends on your needs. The free edition is perfectly good for most people, however there are several features and modules that are only available in the Enterprise Edition. Notably, some of the disaster recovery, scaleout, and multifactor authentication features cost extra.
I think you might be confusing vault with another product?
We self-host vault in production, and it doesn't cost us a dime.
(other than the engineers we pay internally to operate it, of course)