Looking for some help for a trip from Delhi to Meghalaya and Assam

Hey, so I wanna go to Meghalaya and then assam (or the other way around) for a 7-10 day trip. I have never been to North East and don't really know much but off just google I am thinking maybe flight on one way and train on the other. The target for this trip is getting away from the city, the horses of people and the pro max air. I wanna visit places with lots of trees, waterfalls/rivers, and as few people as possible. So, if you guys can suggest hidden/popular spots with these things that would be awesome and more importantly how I get there and where I stay, and even more importantly what would the budget look like... Thanks in advance!