Hi, You can book your stay in Old Manali or Vashisth in advance as it will be peak season. You can choose to stay in Zostel as it is a great option for solo travellers. You can spend 4 days in Rs 5000 easily if you use public transport for Rohtang Pass. You can read more about Manali in the trips and guide attached below. Keep exploring!
Hi @Sooriyaa you must have a look on Manali complete travel guide by Tripoto - https://www.tripoto.com/travel-guide/manali . Here you can explore Itineraries by travelers who alredy been in Manali, hotels, places around.