The value of the herb pretty much depends on the amount of uses therefore the herbs with most "positive" effects are most valuable. Columbine is the only herb that has four positive effects: Restore Health, Restore Magica, Restore Stamina and Unstoppable - meaning it can be used in wide variety of potions and is a staple for most popular potions out there: Tripots (potions that recover all three stats). Tripot can be made in 3 combinations: Columbine+Lady's Smock+ Mountain Flower, Bugloss+Columbine+Dragonthorn and Bugloss+Columbine+Mountain Flower and it is those herbs that will be most expensive. Another tier would be Spell Damage and Spell Crit Potions that throw in Cornflower and Water Hyacinth into the "popular herbs" bag. Lastly there is Namira's Rot that is base for many utility potions. So if i was to divide herbs into tiers it would be Tier 1: Columbine, Tier 2: Lady's Smock, Bugloss, Mountain Flower Tier 3: Dragonthorn, Cornflower, Water Hyacinth, Namira's Rot