Hey is taking $10/month. With $7/month revenue going to them they will still be the most expensive email app available, so I don't see why it would be so hard to stomach.
$99/year != $10/month. It's $8.25/month. Also something like Fastmail is $9/month (or $90/year) with 100GB of storage (which is what HEY provides) - so it's actually pretty competitive pricing.
Sure, $8.25/month, but for fastmail you just picked the most expensive option that most people don't need. $5 is standard pricing.