Since you will still have your local computer running to actually use it, you have to add its electricity costs to the dev machine cloud hosting aswell. You actually also need to buy the local machine to do work anyway, so it doesnt save any money, but adds 300 USD to your current dev enviroment. That said, i can get a plain old Vserver similar to an EC2 mini instance (i think its even more powerful) for 80 bucks a year and that would be running 24/7. If you dont need the benefits of EC2 which are scaling and such, there are much cheaper solutions.