The lower element in our Whirlpool range just went out. The manufacturer's part
number is 380180.

Is there a big disparity in pricing for the same units (same quality), or are
there good parts and crap parts?

For example, compare http://tinyurl.com/65oypz with http://tinyurl.com/5zpnqe.
Why would I want to buy the more expensive part?

Residential grade burglar alarm equipment is sold to the consumer at an
extremely high markup. Is the same true with appliance parts? It seems to be an
extremely competitive business.