One thing to be aware of is, tires age after manufacture.
Even if the tire sits on a rack in a warehouse it continues to age.
So one reason some tires may be lower cost is due to the tire being old.
Most tires have a 4-digit date stamp on the sidewall in the form 2-digit week/2-digit year.
So 0609 is the 6th week of 2009.
I've seen good deals on tires, but were made over two years ago.
Now frankly, I didn't notice much difference.
But it might be important for track tires as the decomposition could have an impact on traction.
I recently bought a set of Pirelli Corsa III's and was told that tire prices are going up dramatically real soon for all brands, possibly this month.
The quoted soon to be MSRP for Pirelli Corsa III 190/55-17 will be over $300, and the 120/70-17 will be over $200.
Now that's full retail. But it will have an impact on all prices.