AWS sells a convenient service, if you cannot afford that service maybe just don't use it?

It's common to hit the time limit before the credit limit.

100k has to be associated with an "Activate Provider" and a few other criteria

My two cents is to build something that could be deployed anywhere else also.

Maybe you are fine staying on AWS forever but maybe you could save a lot of money by migrating somewhere else later.

AWS fees could cost more than your startup makes, depending on how you build your service, who knows what the future brings.

So it's better to make your deployment flexible enough that you can ditch AWS and migrate to dedicated servers easily. It's something to think about from the start.

If that percentage is low, AWS is fine. It's expensive, but it's not worth your time optimizing a small proportion of your cost in an early-stage startup.

My current (not a startup) employer is on AWS and it makes sense for us as it's not a big deal relative to what customers are paying us, and it's an easier sell at the kind of deal size we deal with and our customers often require specific providers.

If it's a high percentage, but you're still at bootstrap level costs, it's fine to stick around for a while - just keep an eye on it and avoid AWS-specific services/lockin.

If it's high, and your costs in absolute terms are starting to bite, then look at your options. AWS is expensive, especially if egress bandwidth makes up a lot of your AWS bill. But you also need to consider your customer base. If it's a B2C business, then nobody cares. If it's a B2B SaaS or similar where your customers are businesses that might assign a lot of trust to AWS or have their own infra on AWS, you need to understand whether or not they care, because worst case any savings will be eaten up by lost business.

In the past, I've worked somewhere that was nicely profitable on cheaper hosting but where the margins meant using AWS would have been certain bankruptcy. And many other places where we made significant savings.

You need to understand your costs well, and whether optimizing hosting is even worth it, in other words, and even if it is worth it at some point, it might not be worth it now.