Hi,
You might want to try SIS - Sales Information System for this. Good old SIS which is now a days not being used by very few people.
I think it has been a while for me on this topic, but I feel there might be some way to track this info without having to create the Z Table that you are thinking of. The Custom Table might be complicated with all the stuff you are thinking of.
I am not saying that SIS will give you the full information the way you are looking for but you will reach half way there.
You might look at the flexible analysis feature of the SIS for this.
Assuming that you are successful in using the Z Table route, you still need to have logic in pricing to be able to compare the different volumes during some time period and do what it has to do in actual pricing during the Order and Billing Transactions. This is going to be the case for both scenarios.
Thanks.
