Spoiler, if you decide to use viam, you will need an API key to make an LED blink. But don't blink the LED in excess of $5/month!
I work at Viam. They bill for usage-based consumption of the cloud platform features like data storage and ML model training. The pricing page says you can "remotely manage machines through Viam web UI" for free, this includes controlling your machine with the SDKs.
Im assuming there are many open source alternatives to do this? Why pay to run edge devices?
All the Viam code that runs on your machines actually is open-source (see https://github.com/viamrobotics/rdk).
You'd pay for things like data collection/storage in the Viam cloud, cloud-based ML training, etc.