Free agents.
Every new season you start go straight into the free agents they will update the system with new youngsters that dont have a club. I sold a 21 year striker after having him for 1 season to PSG for £36million making him the 3rd most expesive player on the game.
I usually sign about 3 young free agents up a season and sell them on, a few of them like Zecchin stay though as they are quailty.
I have £40million in the bank with Blackpool but i dont really need to buy anyone.
Or people who only have 6months remaining on thier contract, I got Rodriguez for £17million and he is currently worth £29million but he is staying he is amazing. Danilo was £4million and he is was worth £9million before he even played a game for me.