Where to buy a cheap windows 10 product to activate my windows 10?

I understand your situation. Buying Windows 10 product key can be expensive, but there are some options to find more affordable or discounted keys legally:

1. Authorized Retailers and Discount Stores:  
Look for sales or discounts on reputable online stores like Amazon, Newegg, or Best Buy. Sometimes, these retailers offer Windows 10 keys at a lower price during sales events.
Be cautious to ensure you're purchasing from authorized sellers to avoid counterfeit keys.

2. Alternative Options:  
If the cost is prohibitive, consider using Windows 10 in unactivated mode for free with some limitations (like a watermark and personalization restrictions). Microsoft allows Windows 10 to run without activation indefinitely, though some features are limited.

3. Microsoft Authorized Resellers:  
Check Microsoft's official reseller list for discounted licenses or volume licensing options if applicable.

Important: Avoid third-party sites offering "cheap" Windows 10 product key that seem too good to be true—they may sell invalid or pirated keys, which could cause activation issues or security risks.