I second that motion.   SQLite isn’t an SQL database server.   What it is, is a public-domain(!) single file format which supports a rather full SQL-database model within that file (or files), including reliable transactions and therefore locking and known-good file sharing.   You don’t have to install anything beyond a package.   Since the database is “just a disk file,” in the same way that the file that you are now contemplating is just a disk file, this approach would give you tremendous “bang for your buck” and I would argue that no proprietary approvals of any kind would be necessary ... even in the most “hardened” business environment.   You are storing the data “in a file,” as originally contemplated, but now that file happens to be an extremely smart file.   Furthermore, the odds that SQLite is already there, even for run-of-the-mill purposes like hosting the cpan modules database, are pretty near 100%.

P.S.:   Yes, I said public domain.   There is no license.