I built an app a few years ago and needed some sort of DB to store around 50 million records that had ~10k reads+writes per month with 1 index. It cost me something like $50 to load it up initially, and then something stupid like 10 cents/month to maintain.
It is the same story over and over again. Your AWS bill is "low" because the actual resources you use are a tiny fraction of what a modern computer can deliver.
This is probably fine for your case, but you could run the same load on any toaster, and without a meaningfully demanding task it is hard to tell them apart.