Amazon usually has lower prices if you have a Prime Membership for free shipping and sometimes no sales tax.
Costco is good if you can use the large amounts before things spoil.
Sometimes companies have cheaper prices through their internet websites than they have through their retail stores.
AllStarHealth has cheaper and more recently manufactured goods than through GNC retail stores.
Shop around (including using the internet) and be an informed consumer before buying.
Peace be with you and everyone, who you love,
Robert