With the recent announcements regarding the licensing model that will be updated sync with October 2019 Wave 2 release, we can see that there's no more "plans" but we get into a situation where you pick the licenses based on the usage.
This way, for user "A" he may only need access to Sales Enterprise while user "B" requires that module plus having access to "Field Service" and so on. The pricing for the modules can be a bit complicated as there's base price and add-on price, plus rules on the different scenarios.
To ease up the calculation, I've posted a sample Canvas App that does that scenario calculation / rules for me 
watch?v=ZCmq2_LW9Wk&t
...