Spain is one of Western Europe's best-value destinations. Budget travelers can manage €55-80/day: hostel dorms run €15-25, a menu del dia (set lunch with starter, main, dessert, and wine) costs €10-14, and many museums are free or discounted in the early morning or on certain days.
Mid-range travelers (€110-160/day) can stay in comfortable hotels, eat at proper restaurants, and take AVE high-speed trains between cities. Intercity buses are even cheaper. Andalusia is notably more affordable than Madrid or Barcelona.