Wow, they are charging you a lot of money for rentals. If you are paying nepali rupees then its extra expensive. Usually they'd rent you a 500cc bullet for around 400 a day here.
But if you are going to spend some time riding and thinking of doing the same in india, why dont you buy a used bike in nepal. It might cost you less than paying rents. Then when you are done, take it back to nepal and sell it off.