Bringing that amont of money to US at one time may be a risky business. I believe there is a restriction on how much dollars you can exchange from rastra bank at one time. It would be lot better to divide it into couple of trips or share it among various family members or friends if they were traveling with you. Try finding people who are traveling to US and willing to help you out. You can also try to exchange your NRS to dollars by contacting businessman or people who returns from US. They may charge you little more than what rastra bank rate is.