Hey Neog, Yessss, you can reach auli from nainital in bus. But it will take more time compared to taxi as there are no direct buses plying in this route. Firstly, take a share taxi or a regular bus from Nainital to Haldwani. this is about 40 Kms. From there take a bus to Haridwar ... this is about 225 Kms and takes approx 6 to 7 hours of time. After you reach Haridwar, u find a lottt of daily buses plying from Haridwar to joshimath and also directly to Auli ...This distance is about 280 Kms and would take 9 hours to reach Auli. So all in total you would need to travel 550 Kms from Nainital to joshimath via bus service and this would also be cheap than car services. Happy Travelling Bro!!!