Various SaaS business models
dasht: I don't know anyone who does it this way but an idea I like would be metered, like Amazon, but with a twist: a safety net and "grace amount" for users:Customer signs up, gives a CC or other payment assurance, says "I am willing to pay up to $N/month for this."Ideally, the customers actual metered usage comes out at $(N-K) and you bill that lesser amount.Suppose on day 15, though, the customer has used up $N.  Instead of suspending them, you float them for three days and alert them.   If they ignore the alert, suspend them after 3 days or a max of $X overage.   The customer can also respond to the alert by saying "please suspend for the month" in which case you eat the overage (< $X).  Or the customer can raise their limit: "Ok, I'm willing to pay $(N+J)."In other words, a kind of "meter with circuit breaker and graceful failure mode".    As a customer, it makes me paranoid that I might, through unforseen causes, rack up way more in some metered charge than I thought just because I didn't check the meter myself for a few days.   The above would fix that.To avoid gaming, you might want to have rollover of overage charges towards the end of the billing period.-t