The dealer's invoice price is not necessarily his real cost. Many times the manufacturers add incentives, offer financing help, and offer model year end assistance. The answer to that question is subjective because the value of the dealer after-sale support is hard to quantify. The specific dealer and or salesperson are also common to the three scenarios. Some dealers do not provide good-after sale service even when they make good profit on the deal.
Some dealers provide great after-sale service no mater how much they make on a specific deal.
Some salespersons have lots of tenacity and will us it to go the extra mile to help you. Some of the better salespersons have a very loyal following of customers and have earned that loyalty by providing after sale service. Evaluating the dealer's service department can help you establish this value. Some service departments are great and some are not. Interview the service manager and get a list of customer references that you can call.