Would my idea be a legal business venture?

My idea involves a regular online store, but instead of buying products for full price, users would pay as much as they wanted for it. For example you could pay $1 for an iPod. Other people are also putting money towards that iPod. I would set the price at $200 and whoever pays the 200th dollar gets the iPod. So, it’s kind of like group shopping because everybody is paying towards the same product. But at the same time it’s kind of like gambling because you don’t know how close that item is to the $200 finish line. You are paying money and hoping to buy (win) the iPod.