Sturridge is probably valued at ~30M right now I would think.
Have to keep in mind that he's quite injury prone.
If he scores 20+ this season, he'll be closer to 35M. He's very good, but he's still quite a bit off the elite strikers of the world.
Keep in mind Higuain moved for around 32M over the summer. Balotelli 26M to Milan, Jovetic 23M, Soldado 26M, Negredo 22M. Mario Gomez went to Fiorentina for just 14M.
Cavani was 57M to a free spending PSG, Falcao 53M to Monaco.