According to https://matrix.org/docs/guides/faq.html#what-are-synapses-platform-requirements For small deployments (<50 active users) around 512MB of RAM is probably okay.
So it’s not like crazy expensive, for the 400 users that are on the L1T discord right now.
4GB ram , i’ll gladly sponsor the ram. upto 1600 users. Which is 4 times as many, right now