Start with quotes: how a member requests one from the cart, how staff price it in the admin, how the member orders it before it expires, and the two member screens a site supplies to list and show quotes. Then prices for groups of customers, which are discounts with a person-group condition, how they combine with a sale, and two patterns for putting an approver before an order, with the size of client each suits.
The last page is for scoping: purchase-order numbers, paying on account, company accounts and contract prices, each with the parts it is built from, so the work is in the estimate from the start. The unit assumes a working checkout and payment step, as built in the earlier units.