Well, it's a tough one to crack. I want the service to be as cheap as possible, and include a free tier as well. I have decided to have the free tier heavily limited in terms of usage, but no functionality is left out.
To tackle multi-account usage, there is a limit on how many free tier accounts are available, plus a usage-decay for non-used accounts to drop out of the free tier. This in turn frees up the limited amount of free tiers.
Haven't seen this before, but fancy the idea a bit. What do you guys think?