10 tips for making high availability more affordable in the public cloud by Dave Bermingham and Joey D'Antoni via @infomgmt

10 ways organisations can utilise public cloud services more cost-effectively while also maintaining appropriate service levels for all applications.

This is a great article.  I would add that you should tune everything very carefully and try to make the best use of the resources you are paying for. If you understand the way the cost structure works and the way your code works being clever and careful with tuning code can potentially save (or waste) a lot of money.