Interest is measured in how many will pay and how much. As said above, you need to talk to your users and figure what features have value and what that is. Rinse and repeat.
We've priced it relatively high at first, but we've also put the language "If you want to get on the paid plan for Hallway, but don't want to pay, just email us at support@hallway.chat with a link to yourself sharing Hallway on social media and we'll give you a discount"