I think the term you're looking for is "a la carte." Nickel and dime sounds terrible. Anyway, I'm personally a fan of subscription based services but monthly,

I think the term you're looking for is "a la carte." Nickel and dime sounds terrible. Anyway, I'm personally a fan of subscription based services but monthly, not annually. People seem to forget annual subscriptions (except for domain names) and these spikes in the budget often have people canceling. If possible or if it makes sense, go the monthly subscription route. In a way, it reminds them to take full advantage of it (so it lets them make it relevant) and you'll have a more stable income as a result. The "buying credits" idea is also a good one. It becomes a pain if they have to pull out their cards too often though.