This could be done without too much trouble in Quickbooks. Set up some non-inventory part items, e.g. sedan, SUV, truck, whatever seems important to categorize. Each vehicle can be tracked by S/N, description, whatever. Each sale to a customer will give you the profit details, including direct costs. Tweaking existing reports to get exactly what you want might be a one time effort, or maybe there are already report templates out there for the asking, I haven't looked.
Whether this qualifies as "easy" is debatable, but certainly it would be well-supported by the marketplace.