The are 5 different ways across 2 unique modes of transportation to help you travel from Valencia to Terrassa. If you're only considering the price, you should check out the bus out of Estación de Autobuses de Valencia towards Estacion de Autobus de Barcelona Norte, as it is the cheapest to Terrassa. It's common to find tickets for as low as $8. ALSA operates from Valencia to Terrassa, so you book your trip with them! Book as soon as you can, as there may be limited availability.
On your trip from Valencia to Terrassa, it is best to book as soon as possible. It won't necessarily help reduce your price by a large amount, but will ensure that you have a spot on the bus or train.