An example: Have an estimate that has client's default PC configuration, plus all the upgrades they could possibly use. Client logs into their portal, opens the estimate when they need it, as many times as they want, chooses the items and quantity they want, omits items they don't want, accepts the estimate, it creates the invoice, and have options to pay for it right then and there. Estimate templates would be customizable for each client, or assignable to groups of clients.