[BeetleB]

Yes, but I want the rate to be variable depending on volume. I want it to be $0.0001 for a simple personal email. But if you send 10,000 emails today, I want it to cost you $100 (or more).

Many schemes to do this. Things like:

The first 10 emails is $0.0001 each.

The next 10 will be $0.001 each.

And so on. You can always fiddle with the thresholds and costs.

[inigyou]

I'm 10000 people sending 1 message each, to get the cheap cost for every message.

[BeetleB]

You're forgetting the 5 cent charge per recipient who hasn't put you in their approved list.