This is what I was told about our costs..
Temporal tables require S3 pricing tier if using DTUs which is about 225/month per database. Also I don't think they work with SQL Express.
Currently in prod we're using dual vCores at a cost of ~540/month. I believe that given our workload we can get away with S1 or 20 DTUS for about $45/month.
My long winded point being that I think we need to fix the prod deployment and spend about $45 per environment right now on MSSQL for a cost of about $180/month for 4 environments.
Using temporal tables will drive that cost to about $1000/month. These are operational and ongoing costs. Think 12k/yr or 60k/5 yrs to audit a few tables feature which is a weak justification.