In summer in Spain, students who failed any subject at school/institutos used to attend private lessons at non expensive estival academias in their towns during July and August. So there were private academias in every town run by older students or teachers. Since 1989/1992 we have a new education law and there are no september exams and these academias closed. In some places, maybe, these academias are still running in summer( for english or computering studies to children). Write to the ayuntamiento.

Anyway, private lessons given by an older student is about 7€/9€ per hour. North Spain is more expensive than south.

Saludos.