Depends on adventure activites you are opting and number of days you are going to stay.
You can also go through my post for an idea. Enjoy travelling!!!
Min 5k to max how much ever u wish to spend depending on the days ur planning to stay and also where u planning to stay.there are many luxuroius hotels in rishikesh on banks of river Ganga where u can get amazing view of mountains and ganges .and also there are options of camping on the river side.which will cost u a less then hotels.and iu will get arnge of adventure activities to do and plz do bargain for the price for river rafting as they do drop prices after a bit of bargaining.if ur ready to spend more.u can also go to jumping heights and do bungy jumping or giant swing or flying fox.but book in advance as u vl hv to wait a lot otherwise.have fun