FormerlyHemlock
Hero
But they say nothing about how much those items are equivalent and how equal players will be with them in their hands, because the point of allowing them to buy magic items is so they can enjoy them, not to make one of them more powerful than the others, if a dose of sovereign glue is way more expensive than a tome of clear thought, the player going for the first is not going to be equivalent to the later, and that is not fair.
They do provide an equivalency scale in the form of rarity.
Face it, 5E is nice in a lot of ways but a lot of the rules are totally bonkers. (Spell design rules for example.) There's no point in complaining about 5E's lack of rules for spending gold on, say, spell research when there is every indication that even if such rules did exist, you'd be better off throwing them away and writing your own. That's not a slam on 5E, it's good at what it is.
If you want a magic item shop, make a magic item shop. +2 quarterstaff with the Guardian property on sale now for a mere 4000 gp, the price of a herd of elephants! Girdle of Storm Giant Strength now accepting bids, currently high bid is 200,000 gold from Manfred von Manley! (Do the PCs bid against him or just quietly cut his throat when he's asleep?)
Honestly guys, official rules are kind of hit-and-miss anyway. Use the good ones, ignore the bad ones, and make up your own where there aren't any good ones--while recognizing that "good" rules are a matter of taste anyway. House rules are always the best but they take more work...