There are a lot of websites that sell CDKEY, which makes it difficult for us to choose. Fortunately, there are also some websites that collect these sales websites for us to view, so that we will not be so blind.

I don't mention some old price comparison websites. I believe everyone knows. Say a website https://www.keydit.com that I discovered recently.
He has collected data about dozens of sales websites. The price is clear at a glance.
You can try it.
Good Luck