I think Kolkata will be cheapest. You can contact me , I will get you in touch with sone manufacturers. firstname.lastname@example.org.
Chennai is other option. But leather is cheapest in Kolkata as compared to Chennai and the major cost in leather jacket is that of leather followed by labour. As such, Kolkata will be a better option.
Kanpur is struggling with leather industry. The main reasin is lack of cow skin and they are relying on buff. Cow skin fetches better price in international market. As such, again Kolkata fetches better as cow skin is easily available here.