Best chatbot to learn

I have used a bunch of chat bots as a customer and want to learn how to create one. I know there are a ton of tools out there but what is the best chatbot to learn that’s also the cheapest to implement into a website? I have seen Manychat which is good but has a month subscription fee and must be logged into via fb or IG account, which I don’t want to do. Are there any cheap or free ones? Or better yet, is there a code I can run on ai to create an easy one for me to put on a website? Thanks in advance 🙌