There's also development and maintenance costs? Someone needs to build that web UI, android and iOS apps, kick those servers when they misbehave, answer the phone or reply to your enquiry?
Except for the apps, cloud hosting providers already give you all of that for a better price. I also don't want an app... IMAP is a standard, you know.
It's cool you spend your time and money doing things you like (regardless of whether those RFCs will be implemented by email servers and clients) but don't make your customers pay for it. Set up donations or something.