Will I have to pay?
Well ask what is important and basically say what you think.
No.
In or out of warranty you can get a free over the counter 'Apple Service Diagnostics' test
Genius reservation http://www.apple.com/retail/geniusbar/
on-line https://getsupport.apple.com/GetproductgroupList.action
check warranty https://checkcoverage.apple.com/
Go from there.
