I'm afraid that the options are limited north of Delhi.
In Manali you can rent Enfields, and a range of indian made bikes, but most of these cannot go outside of Himachal Pradesh state.
We rented a bike from Anu (just outside of Manali near Vashist)
We were lucky as this time of the year his bikes are usually all rented out. We paid 300 rupees per day (3 week hire) It was the first and only enfield we rode, so hard to tell if it was any good. All i can say is that the bikes are tuned to
over the high passes easily, but expect breakdowns. We had issues with wheels, brakes, battery and gear shifing. What I didn't like is that they don't forsee any tools with the bikes for emergency repairs. They were really easy going with the deposit though. here's his contact:
anuautoworks @ hotmail . Com
mobile: 981613378 and 9816172338
comes to me now, you can rent bikes in Leh as well, but the enfields there are real crap compared to what we had. All the people we talked to had breakdowns even on 2 day hires....
As long as you're not in a rush you'll be ok with the enfields, foresee a few days in your schedule for roadside breakdowns, lorry rides into the next town and quests for spares....
If you can: go to pangong lake, it's stunning
you don't stop playing because you get old. You get old because you stop playing