FIFA player prices in FUT are affected by a number of factors. Supply and demand is obvious, the best players in the game have the highest price. However various things can change the prices of players. Performances in real life affect their demand. Also how good they are in FIFA, such as Ben Yedder who was amazing in FIFA 21. English Premier League players usually have a higher price due to the demand for the league. Then there are various SBCs and objectives requiring players during the season which influence price. So always keep an eye on them and the prices of players in your team.