Here's a short bit about on demand vs. spot instances, and management of "credits" on AWS Educate in general.

First, the thing to remember is that the service is giving you a certain amount of credit for free, which is awesome and I'm thankful for, no question.

The thing is, one part of using services like the cloud is evaluating the value proposition -- which is hard to do, as your "balance" is completely opaque.

Take instances, for example. I can spin up on-demand instances, but it's not clear how much these cost per hour. I also know, having helped a friend, that spot instances are less expensive.

On demand instances are solid VMs, which are billed at an hourly rate. Spot instances run on a "market" system, where you allow AWS to spin your instance down if capacity is needed. You can set price thresholds to do processing when it's less expensive. Because AWS has flexibilty of when or if to run your spot instances, there is a reduced rate.

So, for workloads that  you aren't fussy about, you can run them as spot instances. Except, it doesn't seem to work on AWS Educate, as far as I've tried. Spot instances would make the credit they give you stretch further, but doesn't seem to be supported.

And I even understand that SOME services might be out of bounds; that's also fine. But getting weird errors and only being able to sort of tell how much things cost from a clumsy panel doesn't help a lot when trying to understand how much things utilize and cost.
Is this expensive thing worth it? Is this cheaper thing worth the extra trouble? Hard to tell when there is no way to map between them.