Legitimate ones are like $8-12 on ebay I buy them all the time.
What computer are you trying to use this windows on? Like mentioned above, just get a win 10 pro license key from Ebay for about $5 if you need a key. Or contact amazon for a refund.
PCWorld has an overview of how to get cheap or free Windows keys, that are at least likely to be legal: https://www.pcworld.com/article/3400840/how-to-get-windows-10-cheap-or-even-for-free.amp.html