I have no idea how much it is - we get an institution-wide subscription. I know there are discounts for students though...
The system is actually quite ridiculous. The wide majority of the research that is published in these journals have been done on tax money collected from US population. And the population that paid for the research has to pay again to find out what they paid for...
The system is changing, with new some journals (like PLoS) providing free access to all published papers, but it's changing quite slowly.