Regardless of price, all hair dryers have the same basic functions - they have a heating element and a fan which blows the warm air in a concentrated line. Expensive hair dryers just look closer at the details.
Higher end hair dryers tend to give the user more control over how they can use the device. This can look like better temperature control, stronger air flow, lighter units, more accessories, better airflow directionality, and quieter operation. On the other hand cheap hair dryers tend to do the bare minimum.
Like many other categories, cheap products do have a habit of picking one spec and really focusing in on it. With over ear headphones it is bass, with hair dryers it is wattage. A trend we have noticed is that cheaper hair dryers tend to have crazy high wattage. At a surface level this can dry your hair much faster, and therefore looks like solid performance. But, like all heat styling, prolonged exposure these high heat dryers can irreversibly damage your hair.
There are middle grounds between stupid expensive, and dumb cheap. What would we call it..? Middling middle? Anyway, if you're happy to spend up to around $300 there are plenty of hair dryers that give you more control without going all the way up to a $649 Dyson.