The factors that dictate the lifetime costs of an A/C unit will affect you for years to come, that's why they're called "lifetime costs." The quality of the system along with its efficiency are just two factors to consider.
Keep in mind that while you may think you're getting a deal by paying less for a system upfront, you'll usually pay more over the life of the A/C. On the other hand, paying more for a system upfront generally ensures lower lifetime costs.
Here's how the concept breaks down:
Equipment that costs less and is lower in quality generally means high operating costs but a low purchasing cost. Equipment that costs more to purchase and is high in quality means low operating costs but a higher first cost.
Also, a quality installation ensures peak operating performance, regardless of the first cost or lifetime costs of the system.
As you comparison shop and work with your HVAC contractor, run the numbers to determine the lowest lifetime costs by asking yourself these questions: