Pastore, Ganso and Hamsik are great goalscoring midfielders, but also expensive. If you want to spend less Van der Vaart, Modric, Anderson, Thiago, Douglas Costa, Alan Patrick, Jean, Marvin Martin
Hamsik is a beast. From memory his finishing is his best technical stat and he usually gets around 10 league goals a season without injuries. He also develops great mental stats and is a great captain 3-4 seasons in. Pastore can hit 20+ league goals a season however he is a natural CAM and an accomplished CM. A cheaper alternative could be Raul Meireles.
You can get Ganso for around 18-20 first season, he will be a solid 30 goal 30 assist guy right behind the striker every year. Pastore is a beast, scored 50 goals for me in the AMC spot in my current PSG game.