The cheapest source for herbs is POWDERS, next is capsules, next is syrup and the most expensive is tintures.
Powders last for 5 years in a tight capsule kept in a jar, while loose powder in a bag should be replaced yearly with fresh, unless kept frozen in the freezer. Syrup formulas should last for years, while the proper made tincture should last 100+ years and get better with each year old.
Best of all is to fresh pick/dig an herb and chew in the mouth the way the Indians had to. The cost is usually free once you find the plant.