Hrmm. Well my first guess, on the price difference, would probably be the gauge of the extension cord.

Thicker Gauge = More Copper.

More Copper = More Expensive.

16 gauge is the minimum gauge for running a high wattage heater, like a block heater, but that is only considered 'medium duty'. For running generators or high amperage motors you would need heavy duty or ultra heavy duty power cords and those need a lot of copper.

$15 for 16 gauge/32 ft is about right. $60 for a 32 foot cord should be at least a 12 gauge but, idk, sometime getting ripped off is your only B&M option. If that is the case, explore online options for a more fair price...