Nature is full of interesting things with healing or other properties, and fantasy nature especially so.
If you need some herbs for a region, you can use these tables to generate them. A temperate region with solid plant growth may have 2-3 useful herbs available naturally. These will generally be fairly cheap. Herbs that have to be imported will be far more expensive, depending on availability of safe travel.
Foraging takes a day and a 1 in 6 roll (or a very difficult skill check in your system of choice) in most cases.
1: Healing (1D6 HP)
2: Recover memorized spell (level 1-2)
3: Ignore one night loss of sleep
4: Count as a full days food and water
5: Recover from injury 20% faster
6: Additional saving throw against mental influence
7: Additional saving throw against poison or paralysis
8: Additional saving throw against polymorph, petrify or death
3-4: 1 round
5-6: 1D6 rounds
7-8: 2D6 rounds