I think the real question is whether you need a hosted solution like Pinecone, etc, or whether you can run a library yourself (like FAISS). The latter won't cost as much, and is pretty simple to get up and running, but may not scale the same way.
There are some other options in between as well. FAISS is a library, so not suited well for production usage unless a single machine is enough. The variety is wider than SaaS vs library. Tools such as Qdrant or Weaviate are Open Source.
And Qdrant might be launched without spinning a server, as long as you use a Python client. So you can actually start locally with in-memory mode, run your dev environment on-premise and then prod on Qdrant Cloud, if you prefer.
This flexibility is a big draw. I can experiment with in memory, launch with cloud, and move to my own infra if I’m lucky enough to need that kind of scale.