Potassium is available for purchase from Amazon.com and Walgreens. Potassium helps the kidneys, heart and other body organs to function effectively, according to WebMD. It also helps to prevent some conditions, such as heart rhythm disorders.
Prices for potassium supplements differ between sellers, but some sellers, such as Amazon.com, offer lower prices when customers buy two or more similar products. Some sellers offer free shipping options for orders exceeding a certain amount. Walgreens.com offers some products only online or only in stores. The limitation on the amount of potassium to consume depends on a person's age. People also can obtain potassium from foods that include citrus fruits, avocados, milk, potatoes and bananas, notes WebMD.