Minimum 4 days is much needed to explore Rishikesh and Haridwar. The cost of 4N 5D varies between 15k to 25K based on your stay and mode of transport.
Coming to places to visit
Haridwar - Har ki pauri, Mansa Devi mandir, Rajaji park, Patanjali yogapeeth, shop at Bara Bazar, visit Vishnu ghat, Birla ghat and Ganga Arti.
Rishikesh- Lakshman jhula, Triveni ghat, beatles ashram, kaudiyala, neer Garh falls, Bharat mandir, byasi, and Madhuban ashram.
It will cost you around 1000 per person normally including food and fun for 2-3 days if you are not staying in camps, if u are staying in Riverside camps it will cost you around 4000 to 15000 per day including food , fun and rafting. to know more click on the link. - https://ridingyogi.tumblr.com/post/686238472588099584/rishikesh-the-land-of-yoga-culture-and-ganga