I have been looking at doing this, but to do it right you have a couple of factors that drive up your price.
First of all, you need not only the tech, but also the 3rd party evaluation and the processes to keep it safe.
Next, you need a way to validate your customers or you'll get butchered either by the secret services of ANY country you operate in (and that includes Canada and Switzerland), or by public opinion the moment a couple of child abusers use the service to keep themselves away from the police. Privacy is a right, but any sensible organisation ensures it meets the obligations that go with it - it is not a hiding place for law breakers unless that is your intention from the outset. This means more process, lawyers and good local relationships with law enforcement so that any access is lawful. On that topic, throwing away data will preclude the service from being used by business which in some countries needs to keep up to 6 years worth of records and email..
Last but not least you need to run this clean and in plain sight. Whatever you hide is the bit that cannot be trusted. Especially when you make it complex, validation costs go up. Silent Circle is presently far too silent.
There is *no* way you can run this at $20/month unless you seek a volume that will make you break any of the points above - which then negates what you are offering.
Unless , of course, you are *sponsored*..