Hi, the cost and duration of your circuit would depend on what all location do you want to cover and is this circuit is going to be on road of you are going to trek. One of the best possible circuit to cover whole of Himachal is you start from Delhi then head on to Shimla, from Shimla to Kinnaur(covering Chitkul-Sangla and Kalpa), from Kinnaur you should head to Spiti Valley(Key-Kaza-Kibber), after Spiti Valley you should head to Lahaul valley (Keylong-Jispa), from Lahaul Head to Manali doing all the nearby destination like Kasol and Kullu. After Manali you can head to Dharamshala region which includes Palampur, Bir-Billing, Mcleodganj and from there you can head to Dalhousie. This should be your last point in Himachal, you can head to Pathankot from here and get a Delhi bound train. All of these areas can be covered in the public transport, HRTC have a very good service and their buses goes to all these locations.