I really recommend using something like Linode for cheap throwaway, might be a bit more expensive (i.e: 5 per month), but the surprise factor disappears..
You'd have to be doing something extremely small to make a $5 Linode more expensive. AWS might be cheaper for a static site, but as soon as you involve a database you're probably paying more.
AWS is not cheap. A lot of people seem get bitten by this.