Outside of free tier - What is the minimal monthly cost to run APEX in the Cloud?
I'm going to take a shot at this first...
According to the OCI cost estimator here: Cloud Cost Estimator (oracle.com)
If you go for a single instance of an APEX Application development service (which includes I think 1 or 2 ocpu of Autonomus Database) with the minimum 1 Terabyte of data the estimate on oracle.com shows $358.41 /month.
If you choose to run Oracle Standard Edition on a VM with 1 ocpu of AMD processor, 256GB of database storage, 16GB of memory and 712 GB of block volume storage you pay $190.22 /month.
If you can reduce to week days only and maybe 12 hours a day instead of 24 hours, you could get it down to $89.60 /month for the Standard Edition configuration and $207.44 for the APEX as a service configuration.