I'm building an app for an organization with about 150 users. I expect the average user to do 20 r/w operations on the DB in a day. I've never used a DaaS commercially before and was surprised that with a mySQL instance on RDS, this would cost about 0.02 USD per hour, or 14.4 USD per month, for the least powerful DB, which is probably still much more powerful than what I would need. I couldn't find any conventional database that would be significantly cheaper.
On the other hand, DynamoDB with 1 RCU and 1 WCU seems to be promising to be much cheaper - to scale down better, so to say - than relational services.
I would still prefer a relational DB, however - are there any cheaper ones that I haven't found?
P.S. A VM in the cloud like lightsail, with mySQL installed, isn't an option - I don't want to administer the DB. I am also aware of the free tier for AWS but would prefer not using it for this.
I want to inform you that found a standalone DB hosting plan for 10$/month at DigitalOcean added MySql support.