EzekielRaiden
Follower of the Way
Rarity is only secondarily related with price. The most common car models IRL are neither the cheapest nor the most expensive.
For something like cars, which are mass-produced and sold with a relatively fast turnover rate, you're absolutely right. The same can be said for food, for example. Magic items are like neither of these things, and are much more like tools (which is, in fact, exactly what they are--magical tools) in a pre-mass-production society. Crappy pots and pans are much more common, and much less expensive, than high-quality ones, which are more common and less expensive than fancy rare-material ones meant for professional chefs.
In addition, for a variety of reasons, inferior products are sometimes more expensive, like iphones and ipads...
Any such goods benefit from the brand-name effect and/or conspicuous consumption--neither of which meaningfully applies. Chefs don't care if their cookware has a designer's mark on it; they care if it will work as ideally as possible (light weight, ease of use, ease of cleaning, durability, etc.)
Nobody is ever forced to follow the rarity tags strictly.
By that standard, there's never anything wrong with any game ever, because nobody's forced to follow anything in the rulebook at all.
But if the book purports to be useful for play, it better doggone well BE useful, and the rarity categories often fail in that task. A modicum of effort could have fixed it, literally just a few hours' time spent by some random person on the internet. A little more, and it could have been a fantastically useful resource for people running any game, not just D&D, by specifically addressing how one can (or even "should") alter the economic and materiel assumptions of a campaign to help support one or more themes.