Hi there Nick,
Greetings from ShepHertz!
Our free plan limits does allow you to use up to 2 Million messages for a trial period of 1 month while you develop your app and test ShepHertz platform services.
Could you further elaborate on your estimated usage for number of messages? I might be able to help you better then?
Feel free to contact me at firstname.lastname@example.org and I am happy to further assist.