They used to have a 512M droplet for $5. After a few years they upped it to 1G, and you could upgrade for free.
gotcha, I've only been with them for 2 years so it's always been 1G for me
I actually got slightly burned when they did that update. I was doing deployments by "slug" (their term) and the old slug went up to $10/month when they created the new 1GB $5 droplet option. Now my system double checks the price before deploying a droplet.
It was 512M before, then they doubled the specs of every droplet a few years ago.