First, the good news. Prices in Spain are generally reasonable compared with other Western European countries, though your spending power may depend on your exchange rate at any given time, in case you have a different currency than Euro in you country.
99% Spanish banks do not change money or cash traveller’s cheques unless you are a client.
ATMs are your best option to get Euros. You can check with your bank if there will be any fee charges. They are very easy to find in Spain. Just be sure to call your bank ahead of time so that they know you are going to be using your card in Spain. Make sure you bring your 4-digit pins. As far as credit cards go, MasterCard and Visa are widely accepted in Spain, American Express is less common but taken in mayor shops and Discover is rarely accepted.
We definitely recommend that you avoid traveller’s checks, which are really unnecessary for Spain, are costly and can be almost impossible to cash.