>I wish Amazon allowed me to cap spending to say 200USD...

Agreed. We use Google App Engine for our recommendation engine (https://recent.io/) and daily budgets are a core feature -- just tap on the "Application settings" tab.

We use AWS for some additional components of our service that aren't part of the core recommendation engine, and I've been surprised by the lack of a maximum-dollars-per-day setting. Or if there is one, I'm not aware of it.