The cost of magic items very drastically the values. Average range are bellow but, in some cases, can he much higher based on where you buy it. If you can even find them for sell. Some more spatialized items can cost much more.
Rarity Value*
Common 50-100 GP
Uncommon 400 - 1000 GP
Rare 4,000 - 6000 GP
Very Rare 40,000 - 60,000 GP
Legendary 200,000 and more GP
Artifact Priceless
Potions and scrolls (and some other one-shot magic items) are normally 1/10 the price of other magic items.
Attempting to sell items can be hard to do. Most people do not have the money to buy them. The few that do may already have deals or contacts to do so. If you are looking ot make quick money you might get 1/2 value of items at some collectors or well-off merchants.
Armor you also add the price of the armor itself.