Plan to explore North East

Hi all, I'm currently in Guwahati pursuing my education here. Still there is only 4 months fory course completion, and I haven't explored North east, except Shillong and Sikkim. I along with 3 of my friends decided to spend this 4 months to cover most of them of how much we can cover and in budget. So, this January we had a budget of 3K-4K. And we haven't decided for the upcoming months. Could anyone help me out for the January month what places in North east can we see with this expense. Please help me out in this, with a travel plan and on how to reach any place.