Before you ask the wholesale cost of the AC unit , consider this.
Would you ask the restaurant the cost of the eggs and sauage in your breakfast? Would you try to make them prove it? What would be gained by asking the cost of anything?
Be reasonable, not combative. Compare retail, sale, installed price, etc.. Then decide which is the best value, may not be the lowest price.
As always, find the best on Angie's List!