Well --- if you want your test conditions to include Minnesota sleet, snow, drizzle, freezing rain, road chemicals and other assorted crap --- I'm your man.
Local Lowes has the heavier duty AP-30 at $44 on their "early" black Friday sale (35% off). The lighter duty one is actually a bit more - not discounted as much. Is that as good as it gets?
I hope you have something in writing. Otherwise the dealer will "forget" any promises he made. You should insist on a discount in order to address the issue yourself. Trusting a car dealer is not an option.