It's based on total number of registered users: exactly number of rows in jos_users table. We do not want to know what your sales are. That was a clear concern during our public pricing consultation, and that we respect.
Short reply is: we prefer adding features helping you increase your business, while keeping cost very reasonable, than lowering cost and features, which will not help your chances to get your business to sustainable levels.
Long reply is: as replied in another thread off-topic, i'm putting it here, on-topic:
We hear those saying it's to expensive for their business or business model, and understand their point of view and suggestions given. We had initially proposed a pricing model to the community which had taken this in account. However, community voice was 99% against such a (imho fair) "Pay-as-you-earn-and-grow" model. So we listened and adapted our model to the "Pay-upfront-and-then-earn-as-much-as-you-like" model that was requested many times. We even adapted the model to have "levels of growth" in it. Now discussion is done, product is released, and pricing is fixed.
CBSubs is certainly at the higher-end featureset for social membership systems, for a very reasonable price, given its broad featureset and great flexibility, which should allow easily to implement creative ideas to grow the business.
To give you a single unique feature that can easily double revenues, it's not demoed here yet: when user selects a plan, you can automatically nicely unhide sub-plans as upsel proposals ! There are many many more features in 1.0 to allow you to grow your business flexibly, and many more to come in next versions.
My point of view was always and still is that if a business or a non-for-profit can't afford to "invest" a few hundred Euros or dollars into a money-making application, then the probability that the problem is not in the cost of the investment, but elsewhere might be quite high, and that the question of viability should be solved rather sooner than later. Please don't misunderstand me, I'm not critisizing any business model here, just trying to warn in a friendly way that starting a business requires many investments, most are way higher than few 100 EUR, and are way less in the directly productive money-inflow path...
Hope that covers that subject.
Happy to answer any non-pricing related question or idea: e.g. how to help you even more grow your business.