Do you have the September play test packet? There were suggested item costs based on rarity.
Player's Handbook, p144 under 'Selling Treasure':
Magic Items. Selling magic items is problematic. Finding someone to buy a potion or a scroll isn’t too hard, but other items are out of the realm of most but the wealthiest nobles. Likewise, aside from a few common magic items, you won’t normally come across magic items or spells to purchase. The value of magic is far beyond simple gold and should always be treated as such.
Magic Items. Selling magic items is problematic. Finding someone to buy a potion or a scroll isn’t too hard, but other items are out of the realm of most but the wealthiest nobles.
Or perhaps even spontaneous magical item creation, like, "Oh, you just crit the dragon for exactly enough hit points to bring it to 0 while you'd dodged for three rounds on 1 hit point and now you can stabilise the three party members on their last death save! Your sword is now a dragonslaying sword +1!"

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.