Catch bus till Dehradun
But be aware to reach before 5 am as the sole bus in running from Dehradun to Sonprayag at 5:30 am (leave some buffer time for yourself)
Take bus from delhi to dehradun there go to parvatiya dipo (parade ground) there you will find all buses to gharwal reason dehradun to gupt kashi ₹440 gupt kashi to sonprayag ₹60