Don't think much and just go to spiti valley. Its the best place I have ever been to. One of my senior is doing his Phd research in Environmental studies and his research work is based on that valley. He has been there for more than 30times but yet it find it new Everytime.
If Budget is less and you are near by Delhi, Go for Gurso Bugyal trek. Last village of India: Mana Village is 10 kms away from this place along with valleys of flowers. There is home stay in Joshimath for around 500 rs per day and it's worth it.