Football Manager 2020

This is easiest to do using Manchester City. They have a very low record transfer fee received and 12 players that have a higher value. Simply load up Man City and transfer list/offer to clubs the highest value players. The achievement won't pop until the player actually signs a contract and goes to the club. I only accepted offers of $50 million or higher just to be safe.

You can check the record transfer fee received by going to club info->history->records and a list of player values for your team is found in finances->salary->salary commitments