Hi , theses guys at somo santander, http://xpeedinsurfshop.com/escuela.html
always have loads of boards to rent and they have alot of second hand ones too. Speak to Nacho he speaks good english.
Also these guys at Berria near santona http://www.watsaysurfschool.com/clases- ... -cantabria
I reckon you'd be best off buying a second hand one myself if your there for a good length of time, but its up to you.
Check out san vicente de la barquera, cool camp site near the beach and good waves too