One reason for the price fluctuations is that each item is listed as having several different possible suppliers. For instance, if it is coming directly from Amazon for $50 and then sells out from Amazon, they will list it as available from XYZ company for $55 and ZYX company for $60.
Many companies will also ship their product to Amazon and have Amazon's superior fulfillment. For example, I send my bubbatime widget to Amazon and ask them to sell it for me for $30. Amazon takes out their fee and shipping cost and then gives me the profit back on each item they sell. I still own all the product that is stocked in Amazon's warehouse and can ask for it back at anytime. I set my own prices and have to compete against other retailers and Amazon that are also selling the bubbatime widget.