Oracle XE is free for production use, but it only makes sense if a) you are already familiar with Oracle, and b) you have a very small data set: “Oracle Data

Oracle XE is free for production use, but it only makes sense if a) you are already familiar with Oracle, and b) you have a very small data set: “Oracle Database 18c XE supports up to: 3 Pluggable Databases 2 CPUs for foreground processes 2GB of RAM (SGA and PGA combined) 12GB of user data on disk (irrespective of compression factor)”