DO NOT DO WHAT ARQIU SUGGESTED, that is the worst advice.

1. It's STEAM bannable to use a VPN to your price advantage
2. G2A Keys aren't legit, can be taken back, and its also possible to recieve action to your account.

Sites like greenmangaming are verified key re-sellers unlike G2A. If you're looking for sales anywhere, use isthereanydeal.com. It shows a whole list of verified LEGAL sellers for different platforms.