Cheaper tires often have less TPI (threads per inch). Think of TPI is the difference between a shirt made with large strings versus one made with thin strings. Large strings don't flex as easy so tires with less TPI ride and handle rougher. Also having less TPI means there's bigger gaps where things like wires and shards of glass can get through. Of course WHAT the string is made of can make a difference just like a cotton shirt versus a silk shirt.

Unfortunately TPI isn't all that easy to figure sometimes. Gatorskins have 3 layers of 60 TPI belts so they kinda call it 180 TPI. The Grand Prix 4000 S features three fabric plies of 110 TPI for a total of 330 TPI. To me the GP 4000 tire rolls and handles better than the Gatorskins.

It's possible to find tires as low as 33 TPI which usually are very cheap tires.

TPI isn't the end all when buying bike tires, but something to seriously consider.