Feverfew ~ Chrysantheum parthenium or Tanacetum parthenium
$5 per plant in 9cm pot (one left)
Feverfew is a native of South-east Europe and is the champion herb for migraine sufferers. In clinical trials 70% of migraine sufferers improved after eatting the fresh leaf (between a couple of slices of bread, it’s quite bitter). I don’t know how long you would expect to eat it daily but I’m guessing if it helps you won’t want to stop.
Fortunately it grows very well and is easy to grow. Feverfew is a woody perennial which enjoys full sun and can handle a windy site.