Set your budget, look for accommodation and suitable transportation, get some information about the place and how many days it will take to explore it.
Chidambaram and pichavaram are great places...
Madurai is beautiful...
Kerala is another budget destination if u use local transportation and lodges...
Depends on what type of travel you want to have. but mostly, north east could be a little expensive as the travelling part will take time from one state to another. also, just good to know, that if you really want to visit the North East thoroughly, 10-14 days isn't enough. you can maybe focus on 2 states at a time. that way you'll be able to explore more