Wenger rarely spends big on already top class players but he has spent a lot of money on young players with potential.
Henry wasn't cheap when we bought him, Reyes was our biggest signing when we got him, Walcott was a PL record signing and Chamberlain wasn't cheap either.
As a club we don't like spending a lot of money on world class players.
So if Wenger can build Mbappe up as the next Henry or world class striker, it means he and the board won't have to splash out 80m or so on a player like Griezman or Aubameyang, who aren't going to come here anyway.
We are still waiting for a replace,went for RVP and Perez and Welbeck are his two biggest striker signings, so it's clear he isn't going to buy a ready made world class striker, even though we have been desperate for one since we sold RVP.
If we can get Mbappe for around 25m, I think this will be the replacement for Giroud.
But I can't see him being the player to convince Ozil and Sanchez to sign new contracts.