At a small SaaS we were put off by the difficulty getting OracleDB's dev edition installed and working at all. While MySQL (then independent) and Pg were bare bones in comparison, they were very quick to get started, covered what was needed, and no risk of price spikes or time consuming audits. When pain points were encountered with MySQL and Pg there were plenty of flexible options to add into the mix.
Later I saw a competitor being crushed by licensing for Informix when they didn't need more than ~10% of its features.
I think it's very relevant to consider that "enterprise" adjacent databases may not support the licensing you need at scale - but that doesn't mean they don't have great engineering and research teams that are solving really difficult challenges, and those challenges may be highly relevant to your workflows. Go into things with an open mind, if not an open wallet!
IMO startups can get edge by exploiting this information asymmetry. Spending a bit more to solve all your DB problems and buy productivity is a no brainer as they have VC funding but not enough time. A single bad DB outage can be the difference between beating a competitor or losing to them. Ditto for slowly shipping a feature because your senior dev is trying to implement their own message queue engine or other random thing that comes out of the box in other RDBMS engines.
The costs depend what you compare it to. People tend to overestimate it. Cost multipler in Azure is very roughly about 4x, it seems (caveat: am not a cloud pricing expert, comparisons may vary wildly). That doesn't include the cost of bouncers and other hacks that increase the Postgres cost, so it's artificially generous to PG.
If you want better features on the Postgres side then you might look at AlloyDB in Google Cloud which is only 2x cheaper on compute but where storage is actually ~3x more expensive!
The extra money buys you a lot. Not only far more features but you can provision a smaller database because the Oracle DB burst scales in response to load. You are only charged for the extra you use so you can provision for normal load without padding extra for emergencies or peaks. It's a genuine cluster that scales up writes more or less indefinitely without sharding if you design your schema right, that's synchronous multi-write master scaling too so its simple for apps. You don't face OpenAI style problems where the single Postgres master reaches its limits and the whole thing breaks requiring app redesigns. And you aren't just paying for an idle replica: all the capacity you buy can be used for queries. It also uses more efficient algorithms e.g. better MVCC with no autovacuuming problems. And a gazillion other things.
So I think you can easily argue that value delivered is much greater than 2x-4x. The capability gap is much larger than 4x. Especially if you're the sort of startup where a bored dev might start citing Postgres' limitations to justify inventing their own DB infra, or where you hit its scaling limits and have to rearchitect - if that happens you'll never recover the cost difference, Oracle will always be cheaper.
This happens because clouds don't charge databases at licensing+labor value+margin, prices are set at what the market will bear.