You can use a Vodafone Spain SIM and activate a 90x1 plan.
Vodafone: Tarifa plana de Voz 90X1
This means you pay only the 1st minute and can talk up to 90 minutes free.
As far as I know this is not valid for SMS too in contradiction to VF offers in other countries.
This makes sense for long duration calls.
In general
www.blau.es is not bad. 1 minute and 1 SMS is 9,28 VAT incl. to any network. You can buy it at The Phonehouse.
Recharging of nearly all spanish prepaid SIMs is possible at CORREOS, the spanish post offices.