Earlier quoted context omitted.
If you're using a cloud hosting, such as AWS EC2, the added expense of Windows is around 30%. Nothing terribly expensive about that. And you also get credits from Bizspak, that could be used to apply to offset AWS licensing.
But god help you if you need SQL server beyond what express provides. (Web is OK but expensive, "standard" or enterprise? Now that hurts)
Too much drama. Here's pricing for m3.large:
Red Hat: $0.193
Windows: $0.259
Win + SqlWeb: $0.367
Besides, you get several(?) free SQL licenses with BizSpark, if you're so inclined.