I have used https://calculator.aws/ in the past, but to be honest it's difficult to account for the egress costs/networking fees using their calculator. Simple things like networking between Availability Zones/Regions can really creep up in your monthly bills if you don't watch out.

I do track my expenses on a sheet manually, using a ballpark figure. At the end of the month I compare it with my AWS bill. If something seems off, I investigate it further. But I don't try to predict exact figures, more like expected ranges.

I do miss the fixed-cost nature of DigitalOcean/Linode. I didn't have to worry about sudden charges, you pay $20/mo per node and that's it. Lots of bandwidth included.

But for the most part it's fine, as long no bot starts bombarding your services with useless requests, egress costs tend to scale with revenue in my case, as my product's pricing is based on usage.

I also have Cloudflare in front of my AWS stack, it has blocked a few small attacks already, but nothing serious yet.