109 (2271lb/1030kg) is the load rating, S (112mph/180kmh) is the speed rating. Click on the Reading The Tire Size links in any of those two web sites for the definitions.
Why some descriptions include load ratings and some dont, i dont know. The tire industry pisses me off with the way they define their products. Metric and inch units and all these codes. Personaly I wish they would settle with using the metric system but even that still uses inches for wheel diameter. Its pretty crazy really.
But as for this thread, I suspect the 'cheaper' tire was probably an error or a discontinued item.