In this page you can find a lot of variety of sports that University of Valencia offered for their students with prices very accessibles.
Do sport free
If you want to do sport by yourself, Valencia has one perfect parc to run, skate, cycling or practise yoga, tai chi for exaple on the grass.
That parc is : Cauce del rio Turia. In this page you can see the parc and his situation: www.visualvalencia.com