We currently run a marketing automation solution and charge by the number of unique users a message is sent to in the month irrespective of the number of profiles in the account. So a customer may have 5,000 profiles but they only pay for 50 if that’s the number of customers they send a campaign or automation to in the month.The challenge with this is it makes price estimation difficult (we currently can’t even do annual pricing) and we incur costs on total number of profiles in the account and not only the ones engaged. (We have to do customer segmentation for every user profile).We are considering profile-based charging (everyone does this) and the biggest challenge for us is the price difference this will cause for some existing customers. Some customers actively use us for just transactional email analytics and do not send messages so we charge them just for the data events. The new pricing model could mean charging  them up to 15x which is unreasonable. I am also trying to avoid creating a separate pricing for just the transactional email analytics. Products with multiple pricing models can be confusing.I'd appreciate suggestions on how to deal with this? Also, what grace period should we be looking at for migrating customers?(More context is available here: 