"Free", but you can only use them on AWS stuff. AWS makes it nice and easy (and does a bunch behind the scenes for you). Part of that behind-the-scenes is that they have control of the private key on their side. You want to use the AWS generated cert locally, or on another provider, too bad.
Someone else mentioned Azure having a similar offering (I’ve never played with Azure so I can’t speak to it). And if 2/3 of the providers offer it, I’d imagine GCP will at some point as well.
I love how easy it’s becoming to launch SSL. LetsEncrypt did a lot to make it mainstream. I’ve never used LE but I am grateful for their impact on our industry.