Ask HN: What database (and database hosting) to use for small projects?

I just started on a project that will probably have no more than 100 customers, keeping track of basic accounting tasks. I'm now thinking about which database service I will use. Looking at the prices of AWS databases, it will cost me $30 per month just to host the smallest RDS instance in the region of my choice.

When starting out on smaller projects that are hosted in the cloud, which database and database hosting/provider do you use? What service do you think offers the best price to quality ratio?