Any paste that's not just plain silicon grease (llight gray or white kinda liquid , the stuff you find in tiny sealed baggies usually, or very cheap 1-2$ 5ml syringes).

Try Arctic Cooling / Silver  ceramique 2 , mx-2 , mx-4 , or whatever you have available near you that would be around the same price range of those.

Anything cheaper would not be significantly better than what you already have on the stock cooler.

thanks