Cloud Workbench (Building a readymade solution for Cloud Developers)

I started thinking of a Workbench for the Cloud developers to ease their efforts and save some bucks while working with commercial Cloud providers like Amazon.

In Opensource world how seemless is to develop a Cloud ready application (rather amazon ready) and test with end2end features before actually deploy it on the Public cloud..

Here I want to do pretty serious business of developing an amazon ready application with EBS & S3 supports locally that can move back & forth from private to public workspace.. Are any ready made Developer Stack available now, so I can still run instances overnight without fearing of dollars.. Of course like you guys, I also want a sound sleep at night -: )

There're opensource offerings to make a private cloud as more similiar to Amazon, but are those supports all the features like Amazon provides? Or can I simply clone my Amazon Instance (with EBS & S3 intact) to these opensource offerings ? I would say it's 40% yes, 60% no..

Then how to fill the 60% Gap that still to go..