Thanks David! I agree, options 3 and 4 are best, especially for a low number of submits. Even with several per day you would fit safely in the free tier of DataFire or AWS lambda.
Here's a link to fork the above project on DataFire, which should make it very simple: https://app.datafire.io/projects?baseRepo=https:%2F%2Fgithub.com%2FDataFire-repos%2Fcontact-us-base
Once you have the backend running, it should be easy for a dev to create an HTML form that consumes it. Let me know how it goes!