Build a whatsapp chatbot

Hi. I need to develop a chatbot. The chatbot will ping users at regular intervals ( once every 3 days or 7 days) and when the user permits will ask a series of questions (approximately 21). I have shortlisted Gupshup as the platform for developing the chatbot since it allows for cross platform messaging but I am open to other platforms as well ( the cheapest per message being the goal). The 21 questions will be in English or Hindi and has to be answered by selecting one of 4 options. Since it is in Hindi, I will prefer bids from India.
The project needs to be expanded to developing other chatbots. Hence, I look forward to bids in terms of per hour rate. However, it will be good if you can mention how many hours it will take to develop the above 21 question chatbot.