Let's say you only need one email address, and have 3 GB of data to store. For one year of use, this will cost:
This comparison assumes you use the simple pricing plan. Using the advanced pricing plan and the defaults given in the advanced pricing calculator, Purelymail would cost $6.51.
Other companies tend to only state limits for storage (though they likely limit other resource use too), so for comparison we tend to pick the cheapest plan that can store 3 GB (uncompressed).
It's not clear whether other companies charge for message size before or after compression. This comparison assumes uncompressed, but that may be inaccurate. In any case, 3 GB uncompressed is a decent amount of mail that should take years to accumulate.
For Protonmail, this assumes the "Plus" plan, paid in USD at the annual rate. That plan allows up to 5 GB storage.
For Fastmail, this assumes the "Standard" plan, paid at the annual rate. This plan allows up to 25 GB storage.
For GSuite, this assumes the "Basic" plan, which allows up to 30 GB of storage that this comparison does not account for. More importantly, GSuite offers much more than email.
The same goes for Zoho, which this assumes is using the "Standard" plan offering 30 GB of storage.
Hushmail offers up to 10 GB of storage.