Complex sentence: Sánchez signed for Arsenal in July 2014 for a fee reported to be around £30--35 million, becoming the second-most expensive signing in the club's history after Mesut Özil, and also the club's first ever Chilean player.
Split into simpler sentences: Sánchez signed for Arsenal in July 2014 for a fee reported to be around £30--35 million. He became the second-most expensive signing in the club's history after Mesut Özil, and also the club's first ever Chilean player.