Looking to covert travellers cheques in Granad

I have recently moved to Granada, and am looking to convert travellers cheques. I have done it once, and paid 5%, which is a crazy amount. Thus, are there any banks that are known to give a good rate for a lot of money? Or, am I better off just trying to set up an account, when I am only going to be in Spain for 6 months max? Any help would be appreciated.