Cheapest may not be your best value.
Buyer beware of cheap, generic vitamins and supplements that may be short on helpful substances and long on fillers and allergenic compounds. Consumer Labs tests hundreds of vitamins each year to find that over 30% have problems.
For example, more or less of a listed ingredient, or they might not dissolve properly. Learn to read labels and be aware of expiration dates. Know what you are paying for and stick to trusted brands and stores. Remember, when it comes to your good health, the price will be worth it.