Hey Akhilesh, First come to Kochi( Eranakulum). Book hotel or zostel near Fort kochi beach. Then follow this route: Kochi sightseeing->Kochi to Munnar-Munnar sightseeing->Munnar to Thekkady->Thekkady sight seeing ->Thekkaday to Kumarakom-> Backwater houseboat to reach Allepay from Kumarakom.
Ernakulam will be better..since it is the main hub...u can go anywhere from ernakulam Though its not that cheap. u will pretty much be able to manage...and please mention where exactly u plan to go...soo that choosing the point would be easy..i can help u since am a mallu.....
Ernakulam is better option. you can stay there few days in a hotel for cheap rate and cover destinations like fort kochi beach, mattanchery heritage places, mangalavanam bird sanctuary, house boating in alappuzha etc.. then you can go to Mumbai, thekkady if you have time..
Ernakulam is the best for you . you can stay there for some days in a hotel for cheap rate and try to cover your destinations like-mattancherry heritage places, mangalavanam bird sanctuary,house boating ⛵ in alappuzha, fort kochi beach and etc.. Enjoy your tour, happy journey.