It is $50 if you want to reschedule but there may be a deadline to do so for each test date. I'm not sure if there is a limit to how many times you can reshedule. I don't think there is, but I could be wrong.
It's $50. You have to reschedule a minimum of 2 weeks before your test, otherwise you will be forced to void. You can only schedule for test dates this year (ie no 2009 test dates).