There are companies who are identified as providing J-1 visas and they charge $5k - $6k for the service
http://j1visa.state.gov/participants/how-to-apply/sponsor-se...
http://j1visa.state.gov/participants/how-to-apply/sponsor-se...
The main requirement is the US company needs to have at least 25 full time employees -- not sure if YC qualifies.