We started out on our AC bus booked via Redbus from Kashmere Gate ISBT. We had to stop at Anand Vihar to change our bus and it took a lot of getting down and up and a lot of people haggling for seats before we finally left Delhi, en route to Meerut, and could get a sleep. In the morning when we woke up at 6am, we realised, we had only reached Hardwar, a good 40 Kms out from Dehradun. It took us another hour to finally deboard at Dehradun ISBT. And yes we do regret not booking a state bus Volvo, which takes a shorter, more direct route and also less time.
The Dehradun ISBT has a prepaid taxi booth which charges 1250 bucks for a private cab till Mussoorie which is 35Kms uphill from there. We did not take a bus as we were afraid if motion sickness got the better of us on the twisting and turning mountain roads. It was a smooth ride though.