My experiences living in various cities in Spain have shown me that AC is not that big of a deal in Spain, and that heating is more of a priority (at least in the north). You'll find AC in many three-star and up hotels, but residences don't normally have AC, opting for, as you mentioned, "natural air". The concept of which was used by the Romans. The typical moorish-inspired home has a courtyard in the middle, which was uncovered at night so as to let the cool night air in, and covered in the morning to trap that cool, naturally-refrigerated air in. It's my understanding that in many places in Toledo, for example, that this centuries-old practice is still employed.
As far as the power crunch: I usually only had to worry about drought. In all but one case, the apartments I let were furnished with gas appliances, which are supplied by orange "bombonas" or propane tanks. You always had enough hot water as long as you had gas in the bombona. I can't recall the prices though! I do recall them being quite reasonable though.
To give you an idea on rent + utilities: The cheapest piso I rented was in Barakaldo (Vizcaya) where I paid about 6700 ptas./month in 1990 money, plus about 1000 ptas./month in utilities. The most expensive piso, which was also the nicest and in a historic district, was in Segovia, where I paid 14.500 ptas./month in 1990 money, plus utilities, which, since it had electric appliances, totaled about 4000-5000 ptas./month (1990). Adjust for inflation, and hopefully have some idea what the cost is today. Remember that in both cases, the rent was split four ways.
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Ongi etorri!